Bioprinting on sheet-based scaffolds applied to the creation of implantable tissue-engineered constructs with potentially diverse clinical applications: Tissue-Engineered Muscle Repair (TEMR) as a representative testbed

Purpose: This report explores the overlooked potential of bioprinting to automate biomanufacturing of simple tissue structures, such as the uniform deposition of (mono)layers of progenitor cells on sheetlike decellularized extracellular matrices (dECM). In this scenario, dECM serves as a biodegradable celldelivery matrix to provide enhanced regenerative microenvironments for tissue repair. The Tissue-Engineered Muscle Repair (TEMR) technology-where muscle progenitor cells are seeded onto a porcine bladder acellular matrix (BAM), serves as a representative testbed for bioprinting applications. Previous work demonstrated that TEMR implantation improved functional outcomes following VML injury in biologically relevant rodent models.Materials and Methods: In the described bioprinting system, a cell-laden hydrogel bioink is used to deposit high cell densities (1.4 × 105-3.5 × 105 cells/cm²), onto both sides of the bladder acellular matrix as proof-of-concept.Results: These bioprinting methods achieve a reproducible and homogeneous distribution of cells, on both sides of the BAM scaffold, after just 24hrs, with cell viability as high as 98%. These preliminary results suggest bioprinting allows for improved dual-sided cell coverage compared to manual-seeding.Conclusions: Bioprinting can enable automated fabrication of TEMR constructs with high fidelity and scalability, while reducing biomanufacturing costs and timelines. Such bioprinting applications are underappreciated, yet critical, to expand the overall biomanufacturing paradigm for tissue engineered medical products. In addition, biofabrication of sheet-like implantable constructs, with cells deposited on both sides, is a process that is both scaffold and cell-type agnostic, and furthermore, is amenable to many geometries, and thus, additional tissue engineering applications beyond skeletal muscle.

Frontiers in gene therapy for erectile dysfunction

Complete sequencing of the human genome has made possible a new age of molecular medicine. The utilization of sophisticated genomic technologies has important implications to the understanding, diagnosis and treatment of erectile dysfunction. This report will review one aspect of the impact of the genomic revolution on urology, to wit, the preclinical evidence emerging from several laboratories indicating that gene therapy for erectile dysfunction may well provide the first safe and effective application of gene therapy to the treatment of human smooth muscle disease. The molecular targets explored thus far have concentrated largely on manipulating various aspects of the nitric oxide/guanylate cyclase/cGMP system, although genetic modulation of growth factors, calcium sensitization mechanisms and potassium channel expression have also been explored. Cell-based gene therapy techniques are also being explored. The apparent preclinical success of virtually all of these gene-based strategies reflects the multifactorial nature of erectile disease as well as the numerous regulatory mechanisms available for restoring erectile capacity. While technical hurdles remain with respect to the choice of delivery vectors, molecular target validation and duration of efficacy, 'proof-of-concept' has clearly been documented. The ultimate goal of gene therapy is to provide a safe, effective and specific means for altering intracavernous pressure 'on demand', while simultaneously eliminating the necessity for other forms of therapy, and moreover, without altering resting penile function, or the physiology of other organ systems. It is in these arenas that the groundbreaking potential of gene transfer technology to the treatment of erectile dysfunction will be fully tested. In fact, the potential benefits of the application of gene transfer techniques to this important medical problem is just now beginning to be appreciated/recognized.

The successful long-term treatment of age related erectile dysfunction with hSlo cDNA in rats in vivo

PURPOSE

We have previously reported that 1 intracorporeal injection of 100 microg hSlo/pcDNA reversed the effect of aging on erectile function in a rat model in vivo for at least 2 months. We report our further investigations of the amplitude, duration and physiological relevance of this novel gene transfer approach.

MATERIALS AND METHODS

A total of 191 retired breeder Sprague-Dawley rats were given a single intracavernous injection of phosphate buffered saline, 1,000 microg pcDNA, or 10, 100 or 1,000 microg pcDNA/hSlo. The animals were studied 1 to 6 months after injection. The intracorporeal pressure (ICP) response to cavernous nerve stimulation and immunostaining as well as hematoxylin and eosin staining were done to evaluate effector nerve integrity and tissue histology, respectively.

RESULTS

Gene transfer prevented an age related decrease in resting ICP and a physiologically relevant, significant effect on normalizing erection in vivo, as determined by submaximal (0.5 mA) and maximal (4.0 mA) cavernous nerve stimulation. The effects were observed 1 month after transfection and sustained for 6 months at the 100 and 1,000 microg doses of pcDNA/hSlo (p <0.026).

CONCLUSIONS

The physiological manifestations of gene transfer were detected as an amelioration of the age related decrease in resting ICP, and parallel increase in the magnitude of the cavernous nerve stimulated an ICP response to a level at which visible erections were again observed in this rat model of aging in vivo.

The physiology, pathophysiology and therapeutic potential of gap junctions in smooth muscle

Phenotypic variability in smooth muscle cells accounts, in large part, for the incredible functional diversity required of the involuntary hollow organs of the body (i.e., respiratory passages, blood vessels, gastrointestinal tract, urogenital tract, etc.). In all instances coordination of smooth muscle cell responses, that is, contraction and relaxation, is critical to normal organ function. While numerous biological mechanisms exist for coordinating smooth muscle cell responses, intercellular communication through gap junctions represents a common denominator present in all organ systems. In this report, we review the evidence documenting the presence and functional significance of myocyte gap junctions to physiologically distinct organ systems, and furthermore, provide some examples of their putative roles in organ pathology. Finally, we advance the thesis that despite their ubiquity and heterogeneous expression, gap junctions are nonetheless potentially attractive therapeutic targets for the treatment of certain smooth muscle disorders. Their therapeutic efficacy will necessarily hinge on the existence of connexin isoform-selective junctional effects. The overall rationale for targeting the intercellular pathway is therefore analogous to strategies that target other ubiquitously expressed ion channels, such as calcium or potassium channels. Such strategies have proved efficacious for the treatment of a wide range of human smooth muscle disorders including hypertension, urinary incontinence and sexual function.

Potassium channels and human corporeal smooth muscle cell tone: diabetes and relaxation of human corpus cavernosum smooth muscle by adenosine triphosphate sensitive potassium channel openers

PURPOSE

Sustained contraction of human corporeal smooth muscle depends on continuous transmembrane calcium flux through voltage gated calcium channels. K channels modulate corporeal smooth muscle membrane potential and, thus, ultimately affect transmembrane calcium flux. Therefore, we characterized relaxation responses elicited by the K channel modulators pinacidil and levcromakalim on isolated human corporeal tissue strips. We also evaluated the possibility that there may be alterations in adenosine triphosphate sensitive K channel pharmacology/function related to the presence of diabetes mellitus.

MATERIALS AND METHODS

A total of 215 isolated human corporeal tissue strips obtained from 57 male patients with organic erectile dysfunction were investigated. Cumulative concentration-response curves were constructed at half log increments for steady state relaxation responses elicited by pinacidil and levcromakalim on equivalently phenylephrine pre-contracted (to approximately 75% of maximum) isolated corporeal tissue strips. Potassium currents were measured using the cell attached whole cell patch clamp technique on freshly isolated corporeal smooth muscle cells.

RESULTS

A concentration dependent, glibenclamide sensitive relaxation response of phenylephrine pre-contracted corporeal tissue strips was observed for pinacidil and levcromakalim. Consistent with such observations, electrophysiological recordings on freshly isolated myocytes revealed that pinacidil (10 microM.) and levcromakalim (10 microM.) induced whole cell potassium currents that were blocked by glibenclamide (10 microM.). In addition, statistical analysis revealed that phenylephrine pre-contracted corporeal tissue strips from patients without diabetes were more sensitive to relaxation by both compounds than corporeal tissue strips excised from those with diabetes. Furthermore, relaxation responses elicited by pinacidil and levcromakalim were not affected by charybdotoxin or 4-aminopyridine but were completely reversed by KCl or tetraethylammonium chloride.

CONCLUSIONS

These data indicate that the adenosine triphosphate sensitive K channel subtype is likely to have an important role in the relaxation of isolated corporeal tissue strips and, moreover, they are the molecular target for the K channel modulators/openers levcromakalim and pinacidil. Such observations are consistent with the supposition that alterations in the structure/function/activity of these potassium channels may underlie at least some aspects of observed diabetes related differences in tissue sensitivity to K channel modulators.

Bladder injection of "naked" hSlo/pcDNA3 ameliorates detrusor hyperactivity in obstructed rats in vivo

The goal of these studies was to examine the potential utility of bladder instilled K+ channel gene therapy with hSlo cDNA (i.e., the maxi-K channel) to ameliorate bladder overactivity in a rat model of partial urinary outlet obstruction. Twenty-two female Sprague-Dawley rats were subjected to partial urethral (i.e., outlet) obstruction, with 17 sham-operated control rats run in parallel. After 6 wk of obstruction, suprapubic catheters were surgically placed in the dome of the bladder in all rats. Twelve obstructed rats received bladder instillation of 100 microg of hSlo/pcDNA in 1 ml PBS during catheterization, and another 10 obstructed rats received 1 ml PBS (7 rats) or 1 ml PBS containing pcDNA only (3 rats). Two days after surgery cystometry was performed on all animals to examine the characteristics of the micturition reflex in conscious and unrestrained rats. Obstruction was associated with a three- to fourfold increase in bladder weight and alterations in virtually every micturition parameter estimate. PBS-injected obstructed rats routinely displayed spontaneous bladder contractions between micturitions. In contrast, hSlo injection eliminated the obstruction-associated bladder hyperactivity, without detectably affecting any other cystometric parameter. Presumably, expression of hSlo in rat bladder functionally antagonizes the increased contractility normally observed in obstructed animals and thereby ameliorates bladder overactivity. These initial observations indicate a potential utility of gene therapy for urinary incontinence.

Caveolin-1 null mice are viable but show evidence of hyperproliferative and vascular abnormalities

Caveolin-1 is the principal structural protein of caveolae membranes in fibroblasts and endothelia. Recently, we have shown that the human CAV-1 gene is localized to a suspected tumor suppressor locus, and mutations in Cav-1 have been implicated in human cancer. Here, we created a caveolin-1 null (CAV-1 -/-) mouse model, using standard homologous recombination techniques, to assess the role of caveolin-1 in caveolae biogenesis, endocytosis, cell proliferation, and endothelial nitric-oxide synthase (eNOS) signaling. Surprisingly, Cav-1 null mice are viable. We show that these mice lack caveolin-1 protein expression and plasmalemmal caveolae. In addition, analysis of cultured fibroblasts from Cav-1 null embryos reveals the following: (i) a loss of caveolin-2 protein expression; (ii) defects in the endocytosis of a known caveolar ligand, i.e. fluorescein isothiocyanate-albumin; and (iii) a hyperproliferative phenotype. Importantly, these phenotypic changes are reversed by recombinant expression of the caveolin-1 cDNA. Furthermore, examination of the lung parenchyma (an endothelial-rich tissue) shows hypercellularity with thickened alveolar septa and an increase in the number of vascular endothelial growth factor receptor (Flk-1)-positive endothelial cells. As predicted, endothelial cells from Cav-1 null mice lack caveolae membranes. Finally, we examined eNOS signaling by measuring the physiological response of aortic rings to various stimuli. Our results indicate that eNOS activity is up-regulated in Cav-1 null animals, and this activity can be blunted by using a specific NOS inhibitor, nitro-l-arginine methyl ester. These findings are in accordance with previous in vitro studies showing that caveolin-1 is an endogenous inhibitor of eNOS. Thus, caveolin-1 expression is required to stabilize the caveolin-2 protein product, to mediate the caveolar endocytosis of specific ligands, to negatively regulate the proliferation of certain cell types, and to provide tonic inhibition of eNOS activity in endothelial cells.

Schistosoma hematobium soluble egg antigens induce proliferation of urothelial and endothelial cells

Bladder carcinoma accounts for 26% of reported human malignancies in Egypt, and has been strongly associated with urinary schistosomiasis. Nevertheless, the immediate role of schistosomal egg proteins in bladder carcinogenesis is unexplored. We investigated the effects of crude soluble egg antigens (SEA) of Schistosoma hematobium on urothelial cell proliferation. The proliferation of bovine endothelial Endo, human urothelial J82 and smooth muscle SMC cell lines was assessed by low-density growth assays. SEA induced proliferation of both J82 and Endo cells in a dose-dependent fashion, but not SMC. Preboiling or proteinase K treatment of SEA abolished its effect. In addition, SEA enhanced urothelial expression of B-cell translocation protein (BTG1) and human proliferating cell nuclear antigen (PCNA) mRNAs. Given the strong correlation between cell proliferation and carcinogenesis, the findings suggest that crude SEA may play some role in schistosomal bladder carcinogenesis.

Central modulation of the NO/cGMP pathway affects the MPOA-induced intracavernous pressure response

Alterations in the nitric oxide (NO)/cGMP levels in hypothalamic nuclei, including the medial preoptic area (MPOA), regulate critical aspects of sexual behavior and penile reflexes. However, the effects of altered central nervous system (CNS) NO/cGMP levels at the end organ level, that is, on the magnitude/quality of the erection so achieved [intracavernous pressure (ICP) response], has yet to be evaluated. The goal of this report was to evaluate the effects of intrathecal administration of modulators of NO and cGMP levels on ICP responses to stimulation of the MPOA and cavernous nerve in rats in vivo. In all cases, intrathecal administration of compounds that increase and decrease cGMP and NO levels, respectively, was associated with corresponding increases and decreases in the MPOA-stimulated ICP response. Specifically, sodium nitroprusside (SNP), 8-bromo-cGMP, and sildenafil increased the MPOA-stimulated ICP response, whereas N(omega)-nitro-L-arginine methyl ester reduced it. None of the intrathecal treatments had detectable effects on blood pressure or the cavernous nerve-stimulated ICP response, although intravenous sildenafil increased the latter. These data clearly indicate that intrathecal drug administration affects central and not peripheral neural mechanisms and, moreover, documents that CNS NO/cGMP levels can affect erectile capacity per se (i.e., ICP) in the rat model.

Intercellular communication in cultured human vascular smooth muscle cells

Intercellular communication through gap junction channels plays a fundamental role in regulating vascular myocyte tone. We investigated gap junction channel expression and activity in myocytes from the physiologically distinct vasculature of the human internal mammary artery (IMA, conduit vessel) and saphenous vein (SV, capacitance vessel). Northern and Western blots documented the presence of connexin43 (Cx43) in frozen tissues and cultured cells from both vessels. Northern blots also confirmed the presence of Cx40 mRNA in cultured IMA and SV myocytes. Dual whole cell patch-clamp experiments revealed that macroscopic junctional conductance was voltage dependent and characteristic of that observed for Cx43. In the majority of records, in both vessels, single-channel activity was dominated by a main-state conductance of 120 pS, with subconducting events comprising less than 10% of the amplitude histograms. However, some records showed "atypical" unitary events that had a conductance similar to Cx40 (approximately 140-160 pS), but gating behavior like that of Cx43. As such, it is conceivable that the presence and coexpression of Cx40 and Cx43 in IMA and SV myocytes may result in heteromeric channel formation. Nonetheless, in terms of gating, Cx43-like behavior clearly dominates.

Integrative erectile biology. The effects of age and disease on gap junctions and ion channels and their potential value to the treatment of erectile dysfunction

Initiation, maintenance, and modulation of corporal smooth muscle tone are critically dependent upon agonist-induced changes in intracellular calcium levels and mobilization as well as transmembrane calcium flux. The transient control of myocyte excitability and contractility at the cellular level is inextricably linked to membrane potential, which, in turn, is modulated by potassium ion efflux through one of the four known corporeal smooth muscle potassium ion channels. Corporal tissue responses are subsequently coordinated by means of the movement of intracellular second messenger molecules (i.e., IP3, cAMP, cGMP) and ions (i.e., K+ and Ca2+) among the corporal myocytes by means of intercellular communication through gap junction channels. Knowledge of the critical contribution of these interlinking cellular (nonjunctional ion channels [e.g., maxi-K]) and tissue (gap junction channels [e.g., connexin 43]) systems to the modulation of erectile capacity has provided the scientific rationale for the promulgation of the successful preclinical testing of hSlo ion channel gene therapy for the normalization of erectile status in both aged and diabetic rats.

Significant physiological roles of ancillary penile nerves on increase in intracavernous pressure in rats: experiments using electrical stimulation of the medial preoptic area

The objectives of this work were to evaluate the contributions of the ancillary penile nerves to penile erection in male rats in vivo. We investigated the effects of unilateral and bilateral transection of the cavernous nerve (main penile nerve) on the increase in intracavernous pressure (ICP) following electrical stimulation of the medial preoptic area (MPOA) in male rats in vivo. After unilateral or bilateral transection of the cavernous nerve (main penile nerve), the ICP responses showed decreases of 28% and 55%, respectively compared to those ICP responses before transection. In other words, even after bilateral transection of the cavernous nerve, significant increases in the ICP response following central stimulation were observed. In contrast to these findings, the ICP response was completely eliminated following bilateral pelvic nerve transection. These data suggested that the ancillary penile nerves, which originate from the major pelvic ganglia, have a complementary role to the cavernous nerves in the autonomic motor innervation of the penis.

Physiological roles for K+ channels and gap junctions in urogenital smooth muscle: implications for improved understanding of urogenital function, disease and therapy

Smooth muscle cells constitute a heterogeneous collection of effector cells that, by virtue of both their constituency in blood vessels and presence as primary parenchymal cells in diverse tissues, affect the function of all organs. Thus, perhaps it is not surprising that alterations in, and/or dysfunction of, smooth muscle cells are quite common, and responsible, at least in part, for the morbidity and mortality associated with a very wide range of human diseases. These facts point to the necessity for improved understanding of the mechanism(s) governing the control of myocyte contractility (i.e., tone). Such understanding has been rapidly forthcoming in recent years, and has indicated that in many smooth muscle cell types intercellular communication through gap junctions acts in concert with nonjunctional (K+) ion channels to make important contributions to the control of myocyte tone and tissue homeostasis in physiologically diverse organs. Intercellular communication through connexin43-derived gap junction channels and K+ flux through the KCa and KATP channel subtypes, in particular, appear to play prominent roles in this process. The goal of this report, therefore, is to review the data concerning junctional and nonjunctional ion channels on the detrusor myocytes of the urinary bladder, as well as on the specialized vascular myocytes of the corpus cavernosum. The choice of an excitable (i.e., bladder detrusor myocytes) and nonexcitable (i.e., corporal smooth muscle) smooth muscle cell type ensures that the discussion will at least encompass consideration of a large portion of the spectrum of physiological possibilities for the participation of junctional and nonjunctional ion channels in the initiation, maintenance and modulation of smooth muscle tone. A central thesis of this communication is that detailed knowledge of the myocyte- and tissue-specific properties of K+ channels and gap junctions will likely lead to the improved understanding and treatment of human smooth muscle diseases/disorders.

Trypanosoma cruzi infection (Chagas' disease) of mice causes activation of the mitogen-activated protein kinase cascade and expression of endothelin-1 in the myocardium

Chagas' disease, caused by the parasite Trypanosoma cruzi, is an important cause of heart disease. Previous studies from this laboratory revealed that microvascular spasm and myocardial ischemia were observed in infected mice. Infection of endothelial cells with this parasite increased the synthesis of biologically active endothelin-1 (ET-1). Therefore. in the myocardium of T. cruzi-infected mice, we examined ET-1 expression and the p42/44-mitogen activated protein kinase (MAPK)-AP-1 pathway that regulates the expression of ET-1. There was parasitism and myonecrosis in the myocardium of infected C57BL/6 mice. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed elevated mRNA expression of transcription factor AP-1 (c-jun and c-fos) and increased AP-1 DNA binding activity as determined by electrophoretic mobility shift assay (EMSA). Western blot analysis demonstrated an increase in the phosphorylated forms of extracellular signal-regulated kinase (ERK1/2). ET-1 mRNA was upregulated in the myocardium of infected mice. Immunohistochemical and immunoelectron microscopy using anti-ET-1 antibody detected increased expression in cardiac myocytes and endothelium of these mice. These data suggest that ET-1 contributes to chagasic cardiomyopathy and that the mechanism of the increased expression of ET-1 is a result of the activation of the MAPK pathway by T. cruzi infection.

The genetics and immunology of Peyronie's disease

Peyronie's disease (PD) is a condition characterized by localized and often progressive fibrosis and scarring of the penis. This condition has an unknown etiology although several hypotheses have been proposed. These include traumatic, immunologic and genetic causes. We studied the genetics and immunology of PD using both molecular biologic and molecular genetic techniques. Men (n=283) with PD were identified by retrospective chart review of one physician's office practice. These men were contacted by telephone and asked to submit to an interview and blood test for genetic studies. Simultaneously, tissue and cells collected in the laboratory were examined by Western and Northern blot analysis for examination of protein and RNA for expression of HLA. Of the first 107 men contacted, 24 were available and consented to interview and blood testing. The mean age was 60.3 y with an average duration of PD of 4.9 y. One patient had a family history of PD while no patients had Dupuytren's contracture. Twenty patients were considered to have primary disease while four were secondary. Eleven patients had tissue prepared for Northern blot analysis and nine patients were the subject of Western blot analysis. All tissue, both Peyronie's and control expressed class I MHC while no tissue expressed class II MHC. The expression of mRNA of class I MHC was equal for Peyronie's and control patients while the expression at the protein level was less in the PD patients. We conclude that PD may have multiple etiologic agents. One cannot exclude a class II MHC association but in our population, HLA DQ is not expressed. Class I MHC may be involved as the expression of class I MHC protein is different in Peyronie's patients than in controls. Genetic studies are ongoing. International Journal of Impotence Research (2000) 12, Suppl 4, S127-S132.

Gap junctions and ion channels: relevance to erectile dysfunction

The corporal myocyte is a critical determinant of erectile capacity whose functional integrity, in the vast majority of impotent patients, is sufficient to guarantee its relevance as a therapeutic target. As with numerous other smooth muscle cell types, ion channels are important modulators of corporal smooth muscle tone/contractility. As such, the transmembrane flow of ions (ie Ca(2+), K(+) and Cl(-)) plays an important role in modulating membrane potential and contractile status in individual human corporal smooth muscle cells, while intercellular ion flow ensures the functionality of myocyte cellular networks. The integral membrane proteins that selectively regulate many aspects of these critical transmembrane (eg K(+) and Ca(2+) channels) and intercellular (eg gap junctions) ionic movements have been identified. To date, the large conductance calcium-sensitive K(+) channel (ie K(Ca)), the metabolically regulated K+ channel (ie K(ATP)), and the L-type voltage-dependent Ca(2+) channel appear to be the most physiologically relevant nonjunctional ion channels. With respect to intercellular ionic/solute/second messenger movement, connexin43-derived gap junction channels are widely recognized as an obligatory component to normal integrative erectile biology. The presence of an intercellular pathway ensures that individual cellular alterations are carefully orchestrated in the rapid and syncytial fashion required for normal erectile function. This report reviews the known details concerning junctional and nonjunctional ion channels in human corporal tissue, and illustrates how one particular application of this knowledge, that is, preclinical studies utilizing low efficacy gene therapy (ie low transfection efficiency) with the K(Ca) channel has further confirmed the physiological relevance and therapeutic potential of gap junctions and ion channels to erectile physiology/dysfunction. International Journal of Impotence Research (2000) 12, Suppl 4, S15-S25.

Myocardial expression of endothelin-1 in murine Trypanosoma cruzi infection

Chagas' disease, caused by Trypanosoma cruzi, is an important cause of myocarditis and chronic cardiomyopathy and is accompanied by microvascular spasm and myocardial ischemia. We reported previously that infection of cultured endothelial cells with T. cruzi increased the synthesis of biologically active endothlein-1 (ET-1). In the present study, we examined the role of ET-1 in the cardiovascular system of CD1 mice infected with the Brazil strain of T. cruzi and C57BL/6 mice infected with the Tulahuen strain during acute infection. In the myocardium of infected mice myonecrosis and multiple pseudocysts were observed. There was also an intense vasculitis of the aorta, coronary artery, smaller myocardial vessels and the endocardial endothelium. Immunohistochemistry studies employing anti-ET-1 antibody revealed increased expression of ET-1 that was most intense in the endocardial and vascular endothelium. Elevated levels of mRNA for preproET-1, endothelin converting enzyme and ET-1 were observed in the same myocardial samples. Plasma ET-1 levels were significantly elevated in infected CD1 mice 10-15 days post infection. These observations suggest that increased levels of ET-1 are a consequence of the initial invasion of the cardiovascular system and provide a mechanism for infection-associated myocardial dysfunction.

Gap junctions in isolated rat aorta: evidence for contractile responses that exhibit a differential dependence on intercellular communication

Connexin43 (Cx43) is a major gap junction protein present in the Fischer-344 rat aorta. Previous studies have identified conditions under which selective disruption of intercellular communication with heptanol caused a significant, readily reversible and time-dependent diminution in the magnitude of alpha1-adrenergic contractions in isolated rat aorta. These observations have indentified a significant role for gap junctions in modulating vascular smooth muscle tone. The goal of these steady-state studies was to utilize isolated rat aortic rings to further evaluate the contribution of intercellular junctions to contractions elicited by cellular activation in response to several other vascular spasmogens. The effects of heptanol were examined (0.2-2.0 mM) on equivalent submaximal ( approximately 75% of the phenylephrine maximum) aortic contractions elicited by 5-hydroxytryptamine (5-HT; 1-2 microM), prostaglandin F2alpha (PGF2alpha; 1 microM) and endothelin-1 (ET-1; 20 nM). Statistical analysis revealed that 200 microM and 500 microM heptanol diminished the maximal amplitude of the steady-state contractile responses for 5-HT from a control response of 75 +/- 6% (N = 26 rings) to 57 +/- 7% (N = 26 rings) and 34.9 +/- 6% (N = 13 rings), respectively (P<0.05), and for PGF2alpha from a control response of 75 +/- 10% (N = 16 rings) to 52 +/- 8% (N = 19 rings) and 25.9 +/- 6% (N = 18 rings), respectively (P<0.05). In contrast, 200 microM and 500 microM heptanol had no detectable effect on the magnitude of ET-1-induced contractile responses, which were 76 +/- 5. 0% for the control response (N = 38 rings), 59 +/- 6.0% in the presence of 200 microM heptanol (N = 17 rings), and 70 +/- 6.0% in the presence of 500 microM heptanol (N = 23 rings) (P<0.13). Increasing the heptanol concentration to 1 mM was associated with a significant decrease in the magnitude of the steady-state ET-1-induced contractile response to 32 +/- 5% (21 rings; P<0.01); further increasing the heptanol concentration to 2 mM had no additional effect. In rat aorta then, junctional modulation of tissue contractility appears to be agonist-dependent.

Biophysical characteristics of gap junctions in vascular wall cells: implications for vascular biology and disease

The role gap junction channels play in the normal and abnormal functioning of the vascular wall is the subject of much research. The biophysical properties of gap junctions are an essential component in understanding how gap junctions function to allow coordinated relaxation and contraction of vascular smooth muscle. This study reviews the properties thus far elucidated and relates those properties to tissue function. We ask how biophysical and structural properties such as gating, permselectivity, subconductive states and channel type (heteromeric vs homotypic vs heterotypic) might affect vascular smooth muscle tone.

Differential ICP responses elicited by electrical stimulation of medial preoptic area

Recent findings indicate a complex role for the medial preoptic area (MPOA) in modulating penile erection. To further investigate this important area we measured changes in intracavernous pressure (ICP) elicited by electrical stimulation of the MPOA and evaluated the contribution of the cavernous nerve to the ICP responses after bilateral transection of the cavernous nerve (CN). In all experiments electrical stimulation was performed unilaterally in anesthetized male rats. Two distinct patterns of ICP response were seen after electrical stimulation of the MPOA: 1) increases in ICP during electrical stimulation (pattern 1, n = 10 rats) and 2) increases in ICP after electrical stimulation was terminated (pattern 2, n = 10 rats). For pattern 1, increases in ICP during stimulation exhibited a stable plateau without contraction of striated penile muscles, and bilateral transection of the CN eliminated the ICP responses. For pattern 2, increases in ICP observed after stimulation were lower, more variable, and accompanied by significant amplitude variations ("peaks"), caused by contraction of striated penile muscles. Bilateral transection of the CN eliminated the pattern 2 ICP response but did not alter striated muscle contraction. Histological studies documented that pattern 1 and pattern 2 responses occurred via electrical stimulation of the anterior and posterior areas of the MPOA, respectively. Thus both responses appear to result from activation of the CN, but the pattern 2 response apparently involves contraction of the striated penile muscles as well.

K+ channels and gap junctions in the modulation of corporal smooth muscle tone

Changes in the contractile status (i.e., contraction and relaxation) of corporal and arterial smooth muscle cells (myocytes) govern the flow of blood to and from the penis and, thus, ultimately have a major impact on erectile capacity. As with many other smooth muscle cell types, corporal myocyte contractility is inextricably linked to ion channel activity. Corporal smooth muscle cells possess a rich repertoire of ion channels, including calcium, chloride and potassium channels, as well as gap junction (intercellular) channels. Among these, the K(ATP) (i.e., the metabolically regulated K(+) channel) and the K(Ca) (i.e., maxi-K or large conductance, calcium-sensitive K(+) channel) nonjunctional channel subtypes, as well as connexin43-derived gap junction (intercellular) channels, are thought to be particularly relevant to the control of corporal myocyte contractility. In fact, whereas K(+) channels are an important convergence point for modulating cellular function, gap junctions are a major conduit for ensuring coordinated cellular, and thus tissue, function. The evidence documenting the presence and physiological relevance of K(+) channels and gap junctions to human erectile physiology and function is reviewed. Finally, one potentially revolutionary therapeutic strategy that takes advantage of the important contribution of K(+) channels and gap junctions to erectile physiology is described: maxi-K ion channel (gene) therapy.

Gene therapy: future strategies and therapies

Significant advances have been made in the past decade concerning the mechanistic basis for the control of penile erection and the etiology of erectile failure. The combined efforts and accumulated wisdom of urologic scientists and clinicians around the world have ensured that these basic advances have translated into the remarkable success recently observed in the treatment of erectile dysfunction. In fact, erectile function can now be effectively restored in every man with the requisite level of desire and motivation. Nonetheless, all of the currently available treatment options have either limited efficacy, significant and untoward side effects, or both. There is clearly room for improvement. However, improved therapy of erectile dysfunction is dependent on garnering even more precise details concerning the regulation of human corporal smooth muscle tone, and furthermore, on the identification of relevant molecular targets. The next generation of erectile dysfunction therapies, therefore, will necessarily require the application of molecular technologies to the study of erectile physiology/dysfunction. One such application is the utilization of gene therapy approaches. This report outlines the overall goals and promise of gene therapy for the treatment of human erectile dysfunction and briefly reviews a few initial strategies to that end.

Comparative studies of the maxi-K (K(Ca)) channel in freshly isolated myocytes of human and rat corpora

Patch clamp techniques in freshly isolated myocytes from human corpora have documented that the large conductance calcium-sensitive K channel (K(Ca)) subtype represents an important convergence point for the modulation of corporal smooth muscle tone, and therefore, erectile capacity. Other recent studies indicate a similar role for the K(Ca) channel in the modulation of smooth muscle tone in the rat penis. Therefore, the explicit aim of this investigation was to evaluate and compare the characteristics of the K(Ca) channel subtype present in freshly isolated myocytes from rat and human corpora. In short, myocytes isolated from rat and human corpora retain their characteristic morphology and contractility in vitro, as evidenced by light microscopic studies of their respective responses to activation of the alpha1-adrenergic receptor subtype by phenylephrine (PE). Large conductance K+ currents commensurate with the presence of the K(Ca) channel were readily apparent in myocytes from both preparations. I-V curves constructed from cell-attached patches utilizing symmetric KCl solutions revealed the presence of a single channel slope conductance of approximately 200 pS for both rat and human myocytes. 1 mM TEA applied in the bath solution reversibly diminished whole cell outward K+ currents by approximately 50%, and also blocked the unitary K(Ca) channel activity observed in the outside-out patch mode. Addition of 2 mM 8-bromo-cAMP elicited a TEA-sensitive (1 mM) approximately 2-3 fold increase in the magnitude of the whole cell outward K+ currents in rat myocytes. Taken together, these data confirm and extend previous observations and provide strong evidence that the rat corporal smooth muscle K(Ca) channel has many similarities to its counterpart in the human penis.

The effects of alterations in nitric oxide levels in the paraventricular nucleus on copulatory behavior and reflexive erections in male rats

PURPOSE

To examine the effects of altered nitric oxide (NO) levels in the paraventricular nucleus (PVN) on copulatory behavior and reflexive erections in male rats.

MATERIALS AND METHODS

Extracellular nitrite (NO2-) and nitrate (NO3-) levels were measured in the PVN following administration of the NO precursor L-arginine (L-arg, 10 mM), the NO synthase inhibitor N(G)-monomethyl L-arginine (L-NMMA, 10 mM), or Ringer's solution via a dialysis probe to the PVN. The effects of alterations in extracellular NO on reflexive erections and copulatory behavior were assessed.

RESULTS

L-arg administration was associated with significant elevations of extracellular NO2- and NO3- in the PVN, while L-NMMA significantly reduced NO2- and NO3- levels. A corresponding increase in reflexive erections was noted during infusion of L-arg in the PVN, with a corresponding decrease in reflexive erections observed during administration of L-NMMA into the PVN (Student's t test for paired samples, p <0.05). Mount rate was unaffected by infusion of the either L-arg or L-NMMA.

CONCLUSIONS

Altered NO levels in the PVN affected the frequency of reflexive erections, but not the mount rate. These studies contrast with previous observations of the effects of altered NO levels in the MPOA, and support the hypothesis that physiological specificity in the actions of NO on discrete brain nuclei may have important implications to erectile physiology and dysfunction.

Prostaglandin E1 activates the large-conductance KCa channel in human corporal smooth muscle cells

The large conductance calcium-sensitive potassium channel (KCa or maxi-K) is an important modulator of human corporal smooth muscle tone, and therefore, erectile capacity. The goal of this investigation was to evaluate the actions of prostaglandin E1 (PGE1), the most widely used and effective drug for the treatment of impotence, on the activity of the KCa channel, a prominent K+ current present in human corporal smooth muscle. Whole-cell patch clamp studies conducted on short-term cultured and enzymatically dissociated human corporal smooth muscle cells, revealed mean resting potentials of -50.8 +/- 2.1 mV (n = 8) and -34 +/- 4 mV (n = 8), respectively. In the attached-patch configuration, the corresponding single-channel slope conductance values for the KCa channel subtype were 173 +/- 4 pS (n = 8) in cultured cells, and 190 +/- 13 pS (n = 3) in freshly isolated myocytes. Furthermore, voltage clamp experiments revealed that relative to control values, the application of PGE1 to cultured cells (3.3 or 33 microM) elicited an apparent increase in both the open probability (Po; ranging from 1.2-23 fold), and the mean open time (5-6 fold) of the KCa channel at membrane potentials of +90 mV and +110 mV. PGE1-induced alterations in KCa channel activity were also observed in freshly isolated corporal myocytes. In the whole cell-recording mode, statistically significant, Charybdotoxin-sensitive (100 nM) 2-3 fold increases in the outward K+ currents were observed in both cultured and freshly isolated corporal myocytes. The presence of a PKA inhibitor (fragment 6-22 amide; 10 microM) in the pipette tip was also associated with a nearly complete ablation of the observed PGE1-induced whole cell K+ currents. Taken together, these data confirm and extend our previous observations, and indicate that PGE1-induced relaxation of human corporal smooth muscle is related, at least in part, to activation of the KCa channel subtype resulting in cellular hyperpolarization.

Characterization of ATP-sensitive potassium channels in human corporal smooth muscle cells

Potassium (K) channels play a significant role in modulating human corporal smooth muscle tone, and thus, erectile capacity. Recent pharmacological studies indicate that the metabolically-regulated K channel (KATP) may be an important modulator of human penile erection with significant therapeutic potential. The goal of these initial studies, therefore, was to utilize patch clamp techniques to characterize the putative KATP subtype(s) present in cultured and freshly isolated human corporal smooth muscle cells. In the cell-attached patch mode, two distinct unitary K+ currents were identified whose respective conductance values were similar in cultured and freshly isolated smooth muscle cells. In cultured myocytes, the measured conductance values in symmetric KCl (140 mM) solutions were 59.1 +/- 2.7 pS and 18.4 +/- 2.1 pS (n = 5 cells). Under identical experimental conditions in freshly isolated myocytes, corresponding conductance values were 59.2 +/- 3.7 pS and 18.5 +/- 2.4 pS, respectively (n = 4 cells). I-V curves constructed during step depolarization (-60 to +80 mV), revealed a linear I-V relationship for both unitary conductances. Single channel records documented that both conductances were reversibly inhibited by the application of ATP (1-3 mM) to the bath solution in the inside-out attached patch configuration. The unitary activity of both K channel subtypes was significantly increased by the application of pinacidil (10 microM) and levcromakalim (10 microM). Whole cell patch recordings documented a glibenclamide-sensitive, pinacidil- and levcromakalim-induced increase in the whole cell outward K+ current during step depolarization (-70 mV to +130 mV) of 105 +/- 37%, 139 +/- 42%, respectively. These data confirm and extend our previous observations, and provide the first evidence for the presence of KATP channel subtypes in human corporal smooth muscle cells.

Intraoperative electrical stimulation of cavernosal nerves with monitoring of intracorporeal pressure in patients undergoing nerve sparing radical prostatectomy

OBJECTIVE

To explore the utility of intraoperative cavernosal nerve stimulation in facilitating atraumatic nerve dissection during radical prostatectomy, and thus help predict postoperative erectile function.

PATIENTS AND METHODS

Fourteen patients (aged 51-72 years) underwent nerve-sparing radical retropubic prostatectomy (NSRRP); 10 were potent before surgery (group 1), and four had erectile dysfunction (group 2). A multi-acquisition system (MacLab/8e) with a Macintosh computer was used for real-time display and recording of intracavernosal pressure (ICP) during surgery. Nerves were stimulated with a bipolar probe (monophasic rectangular pulses, 10 mA, 20 Hz, 0.22 s) before and after removal of the gland. The follow-up consisted of interviews with patients and their partners' 12-18 months after treatment.

RESULTS

The mean (sem) basal ICP of 8. 0 (2.0) cmH2O remained unchanged during nerve dissection. The mean increase in ICP during electrical stimulation was >50 cmH2O in seven potent patients (group 1) and was sustained as long as the nerve was stimulated. Postoperatively, these seven patients reported erections sufficient for sexual intercourse. However, the three remaining patients in group 1 had pressure rises of <30 cmH2O, of whom two reported partial erections and one reported total impotence postoperatively. The recovery time for erectile function was 6-12 months after surgery. Two patients from group 2 had transient increases in ICP to <40 cmH2O; one had an increase to 20 cmH2O and one had no response at all. All four patients remained totally impotent postoperatively. There were no complications.

CONCLUSIONS

Intraoperative electrical stimulation of the cavernosal nerves with ICP monitoring before and after NSRRP is a safe and reliable method for documenting nerve continuity and its functional status. Patients who have normal preoperative erectile function and show an adequate rise in ICP upon electrical nerve stimulation during NSRRP will almost certainly be potent after surgery. This tool may be used to facilitate atraumatic nerve dissection during NSRRP.

The putative mechanistic basis for the modulatory role of endothelin-1 in the altered vascular tone induced by Trypanosoma cruzi

Chagas' disease, caused by Trypanosoma cruzi, is an important cause of heart disease in Latin America. T. cruzi-induced microvascular compromise, in turn, is thought to play a major role in chagasic heart disease. Previous in vitro studies have implicated endothelin-1 (ET-1) as a potentially important vasomodulator present in increased levels in the supernatant of T. cruzi infected cultured human umbilical vein endothelial cells (HUVEC). Thus, the goal of the present investigation was to further evaluate the potentially important contribution of ET-1 to T. cruzi-induced alterations in vascular tone in vitro. Bioassay studies once again documented that exposure of isolated rat aortic rings to infected HUVEC supernatants elicited contractile responses whose steady-state magnitude was significantly greater than contractile responses elicited by exposure of aortic rings to uninfected HUVEC supernatants. Furthermore, the increased aortic contractility was significantly attenuated by the presence of the ET(A) subtype selective antagonists BMS-182,874 or BQ-123. Additionally, incubation of HUVEC with either verapamil or phosphoramidon prior to infection was also associated with reduced aortic contractility, upon exposure to the supernatant. Phosphoramidon, but not verapamil, produced a significant decrease in the measured ET-1 levels in the HUVEC supernatant. Consistent with the bioassay results, preincubation of Fura-2-loaded cultured rat aortic vascular smooth muscle cells with verapamil resulted in a near complete ablation of ET-1-induced transmembrane Ca2+ flux. Taken together, these data are consistent with the hypothesis that ET-1-induced vasoconstriction may play an important modulatory role in the vascular compromise characteristic of T. cruzi infection.

Further evidence for the selective disruption of intercellular communication by heptanol

The lack of selective gap junctional uncoupling agents has hampered evaluation of the contribution of intercellular communication to pharmacomechanical coupling and vascular contractility. Thus we further explored the utility and selectivity of heptanol as a gap junctional uncoupling agent in isolated rat aortic rings. Fifty-two aortic rings were obtained from 15 rats and were precontracted to approximately 75% of maximum with phenylephrine (PE). When contraction achieved steady state (approximately 5 min), a single concentration of heptanol (200 microM) was added to each aortic ring at 1- to 3-min intervals for up to 42 min post-PE addition. At early time points (5-10 min after PE), heptanol elicited an approximately 50% loss of tension (i.e., relaxation). At subsequent time points post-PE, a gradual and time-dependent decrease in the magnitude of the heptanol-induced relaxation was observed until, after approximately 40 min, addition of heptanol was associated with little, if any, detectable relaxation. Linear regression analysis of the magnitude of the heptanol-induced relaxation vs. the square root of the elapsed time interval (from addition of PE) revealed a highly significant negative correlation (P < 0.001, R = 0.81). Studies conducted on KCl-precontracted aortic rings revealed no detectable heptanol-induced relaxation after development of the steady-state KCl-induced contraction. These data extend our previous observations to further document the potential utility of heptanol as a "relatively selective" uncoupling agent.

Analysis of the presence and physiological relevance of subconducting states of Connexin43-derived gap junction channels in cultured human corporal vascular smooth muscle cells

Subconductance states are a commonly observed feature of gap junction channels. Their overt frequency and consistent appearance in both single and multichannel records have led to speculation that they might be of physiological importance in terms of altering the rate of small solute transfer from cell to cell. Among the connexin gene family, connexin43 (Cx43) is the most ubiquitous connexin that has been shown to generate subconductive states. Therefore, it was the explicit aim of this investigation to more fully evaluate the potential contribution of human Cx43-derived subconducting states to intercellular communication in cultured human corporal vascular smooth muscle cells. To determine the weight of subconductive states in our records, we analyzed amplitude histograms of multichannel and single-channel data during the application of transjunctional voltages larger than expected for physiological conditions but still smaller than transjunctional voltages known to induce lower conductive states (Vo>Vj). The data clearly indicated that the subconducting states occupy only a small fraction of the total channel open time. This was reflected by the fact that the average open probability for the subconductive state(s) determined from the 9 records analyzed was approximately 2%. Closer inspection of the data revealed that the frequency of subconductive states was actually higher than the frequency of the main state conductance. In summary, recording conditions sufficient for evaluation of the intrinsic gating characteristics of human Cx43-derived gap junction channels have been used. Under these conditions, our data clearly indicate that despite their greater frequency, the duration of subconductance events is so short relative to the main state duration as to render them physiologically insignificant.

Sildenafil: a new oral therapy for erectile dysfunction

Sildenafil citrate (Viagra) is a relatively selective 5-phosphodiesterase (PDE) inhibitor. It is the first oral medication approved for the treatment of erectile dysfunction (ED). The neuronal release of NO which binds to the heme-containing region of guanylate cyclase increases levels of cGMP. This leads to a cascade of reaction which results in corporal smooth muscle relaxation and penile erection. Sildenafil causes an erection by inhibiting PDE5, which in turn causes an increase in the intracellular levels of cGMP. Sildenafil is well absorbed after a single oral administration with a t(1/2) of approximately 4 h. The mode of onset varies from 0.5-4 h. The drug has been used in millions of men since first approved by the U.S. FDA 1 year ago and has revolutionized the approach to, and therapy of, erectile dysfunction.

A stretch-sensitive Cl- channel in human corpus cavernosal myocytes

With the patch clamp method we demonstrate a stretch-sensitive Cl- currents as well as stretch-sensitive Cl- channels in a small group (5%,n 117) of cultured human corpus cavernosal muscle cells. The current and the channel activities had the following characteristics: (1) Their equilibrium potentials changed with extracellular Cl- concentration close to that predicted by Nernst equation provided that the relevant channels had high permeability to Cl- but low permeability to acetate ions; (2) They were blocked by mM concentrations of Zn2+; (3) The i-v relation of single channel current was almost linear for holding potentials varied from -70 to +60 mV; and (4) The channels had unitary conductances of approximately 140-170 pS.

Endothelin-1 as a putative modulator of gene expression and cellular physiology in cultured human corporal smooth muscle cells

PURPOSE

Increases in cytosolic calcium levels trigger smooth muscle contraction while nuclear calcium increases are thought to regulate gene expression. Endothelin-1 (ET-1) affects both. The goal of these studies was to further investigate the importance of ET-1 to corporal physiology by examining its actions on proliferation and immediate early gene (IEG) expression in cultured human corporal smooth muscle cells.

MATERIALS & METHODS

Early passage (1-3) smooth muscle cells were grown in culture and exposed to either phenylephrine (PE) or ET-1 in the absence and presence of serum, the ET(A) or ET(B) selective antagonist BQ123 or IRL1038, or the L-type Ca2+ channel blocker, verapamil. Cell proliferation was assessed with a hemocytometer. The effects of ET-1 on c-myc and c-fos were evaluated using Northern blot analysis. Parametric or nonparametric statistics were used as appropriate.

RESULTS

Addition of ET-1 (100 nM) to serum-starved cultured corporal smooth muscle cells was associated with a nearly 2-fold increase in cell number, as well as 2 to 6-fold increases in c-myc and c-fos levels. Cellular proliferation was inhibited by ET(A)- or ET(B)-receptor subtype blockade with BQ123 (1 microM) or IRL1038 (1 microM), respectively, or blockade of Ca2+ channels with verapamil (10 microM). PE (3 microM) had no detectable effect on smooth muscle proliferation.

CONCLUSIONS

Cell proliferation was mediated by activation of the ET(A) and ET(B) receptor subtypes, dependent on transmembrane Ca2+ flux, and correlated with significant increases in c-myc and c-fos mRNA levels. These studies extend previous observations to indicate the potential pleotropic actions of this peptide in the regulation of human corporal smooth muscle physiology in vivo.

Molecular studies of human connexin 43 (Cx43) expression in isolated corporal tissue strips and cultured corporal smooth muscle cells

Intercellular communication plays an important role in erectile function. The goal of this study, therefore, was two-fold. Firstly, to determine if cultured corporal smooth muscle cells provide a valid model system for evaluating the role of junctional communication to erectile physiology, and secondly, to explore the possibility that there may be age-related alterations in Cx43 mRNA expression. Human corpus cavernosum tissue was obtained from 31 patients with a mean age of 58 (range 27-89), while cell cultures were developed from 21 distinct patients with a mean age of 57 (range 26-59). Northern blots revealed that mRNA for Cx43 was expressed at detectable levels in all samples examined. It migrated as a transcript with an apparent size of 3.1 Kb. Western blots revealed the presence of multiple bands of Cx43 protein in both tissues and cells. However, Cx43 protein in tissue predominantly migrated as a 45 kDa band, while the Cx43 from cultured cells predominantly migrated as 41 kDa band. Cx43 mRNA expression was similarly heterogeneous in both frozen tissues and cultured cells. An approximately 3-5-fold increase in Cx43 mRNA levels was observed in cultured cells relative to frozen tissue, but the expression of Cx43 mRNA was not further altered upon passaging (p1-5). When Cx43 mRNA levels were normalized, and expressed as a ratio of the Cx43/beta-tubulin mRNA, there was a significant negative correlation between patient age and Cx43 levels on frozen tissues, but not on cultured cells. We conclude that: (1) There is similar heterogeneity/variability in Cx43 mRNA levels in frozen tissues and cultured cells derived from human corpus cavernosum. (2) That the expression of Cx43 mRNA in cultured cells is sufficiently stable, and similar to, expression levels in tissue as to provide a valid and physiologically relevant model system for further studying the role(s) of Cx43 in the regulation of penile erection. (3) There is a statistically significant, albeit modest, negative correlation between the Cx43/beta-tubulin ratio and patient age in frozen corporal tissue strips, but not on cultured corporal smooth muscle cells. Such observations provide further evidence for the plasticity of intercellular communication in the erectile process. Moreover, the similarities in the apparent regulation of Cx43 mRNA levels and that of the putative 'housekeeping' gene beta-tubulin, may suggest that Cx43 is constitutively synthesized in this tissue.

Intracorporal injection of hSlo cDNA in rats produces physiologically relevant alterations in penile function

The Ca2+-sensitive K+ channel (maxi-K+) is an important modulator of corporal smooth muscle tone. The goal of these studies was twofold: 1) to determine the feasibility of transfecting corporal smooth muscle cells in vivo with the hSlo cDNA, which encodes for the human smooth muscle maxi-K+ channel, and 2) to determine whether transfection of the maxi-K+ channel would affect the physiological response to cavernous nerve stimulation in a rat model in vivo. Intracorporal microinjection of pCMVbeta/Lac Z DNA in 10-wk-old rats resulted in significant incorporation and expression of beta-galactosidase activity in 10 of 12 injected animals for up to 75 days postinjection. Moreover, electrical stimulation of the cavernous nerve revealed that, relative to the responses obtained in age-matched control animals (N = 12), intracavernous injection of naked pcDNA/hSlo DNA was associated with a statistically significant elevation in the mean amplitude of the intracavernous pressure response at all levels of current stimulation (range 0.5-10 mA) at both 1 mo (N = 5) and 2 mo (N = 8) postinjection. Furthermore, qualitatively similar observations were made at 3 mo (N = 2) and 4 mo (N = 2) postinjection. These data indicate that naked hSlo DNA is quite easily incorporated into corporal smooth muscle and, furthermore, that expression is sustained for at least 2 mo in corporal smooth muscle cells in vivo. Finally, after expression, hSlo is capable of measurably altering nerve-stimulated penile erection. Taken together, these data provide compelling evidence for the potential utility of gene therapy in the treatment of erectile dysfunction.

Endothelin-1-induced alterations in phenylephrine-induced contractile responses are largely additive in physiologically diverse rabbit vasculature

Endothelin-1 (ET-1) is an important modulator of vasomotor tone that is thought to participate in the etiology of cardiovascular disease by virtue of its ability to amplify the contractile responses of vascular smooth muscle cells to the effects of other vasoactive agents. Despite this fact, few studies have quantitated the expected contribution of ET-1 to the enhanced contractile responses elicited in the presence of another spasmogen. As a first step in this direction, ET-1 and phenylephrine (PE) were used to evaluate the effects of co-activation of the ETA/B or alpha-1 adrenergic receptors, respectively, on contractile responses in isolated rings of rabbit aorta, mesenteric and femoral artery, or strips of corporal tissue. Cumulative steady-state concentration-response curves (CRCs) were constructed to PE alone before the construction of a CRC to ET-1 alone, or a mixture of PE and ET-1 using a previously described drug concentration paradigm. Computer fits of the logistic equation to CRC data revealed that in all vascular tissues examined, the partial substitution of PE with ET-1 was associated with a significant vessel-dependent approximately 3- to 30-fold leftward shift in the CRC (P < .01, Student's t test for paired samples), as judged by a significant increase in the pEC50 (negative logarithm of the concentration of drug that elicits one-half of the calculated maximal effect), in the absence of any detectable effect on the calculated maximal contractile response (Emax) or the slope factor (rho). A theoretical CRC constructed using the Pöch and Holzmann method for equiactive substitution demonstrated that the responses to mixtures of PE and ET-1 were often the result of simple additivity of agonist effects in these preparations, and thus, were "expected" based on detailed knowledge of the individual effects of these two agonists. Regardless of the precision of the Poch and Holzmann CRC in predicting the effects of this drug mixture in these vascular tissues, comparison of the "expected" contractile response with the "observed" response represents an important first step toward establishing a more uniform nomenclature for describing the physiological/pathophysiological effects of mixtures of drugs on diverse vasculature.

Neuronal innervation, intracellular signal transduction and intercellular coupling: a model for syncytial tissue responses in the steady state

A model tissue is proposed in which chemically responsive cells are interconnected by gap junctions and innervated by the autonomic nervous system. The model is explicitly dependent on the following physiologically relevant assumptions: (1) a fraction of the cells are directly innervated, and these cells respond to a periodic neuronal stimulus (i.e. the release of neurotransmitter) by production of an intracellular substance (i.e. second messenger molecule); (2) production of second messenger molecules modulates the amplitude of a cellular response, such as contraction or secretion; (3) intracellular formation of second messenger molecules in innervated cells is proportional to the periodicity of the neuronal stimulus, while the intracellular concentration in non-innervated cells is governed by the half-life of the second messenger molecule and the extent of cell-to-cell coupling; (4) the amplitude of the graded response of the individual cell is related to the intracellular second messenger concentration by a Michaelis-Menten function; (5) the amplitude of the graded tissue response is a function of the innervation density, the frequency of stimulation, and the extent of intercellular coupling. Thus, a stimulus-response relationship was developed, where the magnitude of the tissue response was described as a function of the total tissue stimulus. The predicted stimulus-response curve was encapsulated by two parameters: (1) the Hill-exponent, which reflects the steepness of the stimulus-response curve; and (2) the location of the stimulus-response curve, or the half-maximally effective stimulus. Both random and uniform neuronal innervation patterns were considered in model tissues with various effective dimensions. The simulations were also applied to a realistic model of vascular tissue. The shape of the stimulus-response curve is critically dependent on the geometry of innervation. For physiologically relevant (10-90% over 2-3 orders of magnitude) dose-response curves, the model yields an implicit relationship between three different dimensionless parameters. If, in a system, two of these parameters are known, the model can be used to bracket the possible range of the third parameter.

Integrative erectile biology: the role of signal transduction and cell-to-cell communication in coordinating corporal smooth muscle tone and penile erection

The contractility of corporal smooth muscle plays a critical role in the entire erectile process in man. Moreover, in the absence of severe vascular disease, or congenital or other structural abnormalities/malformations, relaxation of the corporal smooth muscle is both necessary and sufficient to elicit a sustained erection. As such, understanding the initiation, maintenance and modulation of corporal smooth muscle tone is an absolute prerequisite to the improved understanding, diagnosis and treatment of erectile dysfunction. Despite this fact, identification of both the precise mechanistic basis by which endogenous and exogenous vasomodulators exert their effects on individual corporal smooth muscle cells, and moreover, the process by which these signals are spread among the diverse array of parenchymal cells in the paired corpora, remains somewhat of a physiological enigma. Therefore, the goal of this report is two-fold: first, to review current knowledge of the regulation of corporal smooth muscle tone at the cellular and molecular level; and second, to outline a cogent explanation for the rapid and syncytial integration of the effects of diverse stimuli among corporal smooth muscle cells in the human penis.

On the putative mechanistic basis for intraoperative propofol-induced penile erections

Propofol is an hypnotic drug used in anesthesia which was noted to induce marked vasodilation in vivo and in vitro, and to elicit intraoperative penile erections. The goal of this study was to assess the putative mechanistic basis for this later observation by confirming its action in vivo in a rat model of penile erection, as well as by studying its effects in vitro on cultured human corporal smooth muscle cells and isolated corporal tissue strips. In vivo experiments were conducted on Fisher 344 rats anesthetized with sodium pentobarbital or propofol. Intracavernosal pressure was recorded during current stimulation of cavernous nerves. A significant increase in the intracavernous pressure response was recorded at all levels neurostimulation, ranging from 1-10 mA. In vitro experiments were conducted utilizing digital imaging microscopy to assess the effects of propofol (3-12 micrograms/mL) on ET-1-induced (50 nM) intracellular Ca2+ transients [Ca2+]i in Fura-2-loaded cultured human corporal smooth muscle cells (passage 3-4) as well as to evaluate the effects of propofol on phenylephrine (PE)-induced contractile responses on isolated corporal tissue strips. With respect to the former, resting cytosolic calcium levels were not altered during preincubation with propofol alone at clinically effective concentrations (12 micrograms/mL). However, propofol produced a concentration-dependent decrease in the peak amplitude of the transient ET-1-induced (50 nM) [Ca2+]i response (P < 0.001). Preincubation of the cells with calcium free/EGTA (1 mM) buffer produced a reduction in the peak amplitude of the ET-1-induced [Ca2+]i transient (55.5 +/- 6% (n = 10 cells, P < 0.01)) which was indistinguishable from that produced by 8 micrograms/mL of propofol (53.4 +/- 5.6% (n = 12 cells, P < 0.01)). However, propofol had no effect on the histamine-induced [Ca2+]i response. Lastly, preincubation of isolated human corporal tissue strips with propofol (100-200 microM; 30 min) caused a significant diminution in the peak amplitude of the PE-induced contractile response. Taken together, these data indicate that the mechanistic basis for intraoperative penile erections observed with propofol may be related, at least in part, to altered transmembrane calcium flux through voltage-dependent calcium channels, and thus, decreased corporal smooth muscle tone.

The "syncytial tissue triad": a model for understanding how gap junctions participate in the local control of penile erection

Recent findings from both clinical and experimental studies document the importance of syncytial relaxation and contraction of corporal smooth muscle to penile erection and detumescence, respectively. However, the mechanism(s) permitting coordinated response generation among the vast array of largely inexcitable corporal smooth muscle cells is unclear. In this report the compelling evidence for a major role of intercellular communication through gap junctions to erectile function is reviewed. Moreover, a novel concept is advanced to explain more fully the putative mechanistic basis for integrative erectile tissue biology. Specifically, the presence of gap junctions, in concert with the autonomic nervous system and myogenic intracellular signal transduction mechanisms, is postulated to form a "syncytial tissue triad" that is largely responsible for the local modulation of corporal smooth muscle tone. It is reasonable to assume that the existence of this "syncytial tissue triad" confers a plasticity, adaptability, and flexibility to erectile function that may well account for the observed diversity of mechanisms known to regulate penile erection as well as the multifaceted etiology of erectile dysfunction.

Reduced connexin 43 expression in high grade, human prostatic adenocarcinoma cells

Gap junction-mediated communication is required for normal cellular growth and differentiation. As cancer is thought to be a manifestation of the breakdown of cell-cell communication, with the concomitant loss of growth control, it would be expected that alterations in the primary structure, processing, oligomerization or trafficking of connexin (cxn) molecules would have a profound effect on the neoplastic process. Here we a present a preliminary immunohistochemical and molecular analysis of cxn 43 expression in prostatic epithelial cells from resected human tissue. Our data indicate that benign prostatic epithelial cells express cxn 43 protein, but that this expression is diminished in more advanced, anaplastic cancer cells. These data suggest that decreased connexin expression is not involved in the initiation of prostate cancer, but rather occurs during the progression of the disease.

Effects of verapamil on acute murine Chagas' disease

Continuous administration of verapamil significantly reduced the mortality rate of acute murine Trypanosoma cruzi infection (P < 0.05). The mechanistic basis for these observations was investigated. Verapamil and other calcium-channel blockers did not inhibit the growth of epimastigotes in culture. Furthermore, verapamil did not inhibit the intracellular growth of amastigotes in endothelial cells as determined by the uptake of 3H-uracil. There were no significant differences in parasitemia between infected mice that were untreated and those treated with verapamil. Twenty days postinfection infected, untreated mice had a parasitemia of 5.8 x 10(6) trypomastigotes/ml (SD +/- 2 x 10(6)), whereas infected, verapamil-treated mice had a parasitemia of 2.2 x 10(6) trypomastigotes/ml (SD +/- 0.5 x 10(6)). There was no significant difference in mortality between mice administered verapamil only for the initial 10 days of murine infection compared to those treated continuously. A 3-day delay in the initiation of verapamil administration reduced the mortality rate, but a 10-day delay did not. Propranolol (beta-adrenergic blocker), prazosin (alpha 1-adrenergic blocker), and diltiazem (another calcium-channel blocker) reduced the mortality but not significantly (P = 0.07). In biochemical studies of the beta- adrenergic signal transduction complex, we determined that verapamil and propranolol reversed the infection-associated decrease in myocardial beta- adrenergic adenylyl cyclase activity. In contrast, complementary western blot analysis revealed no significant changes in the G-proteins of the beta- adrenergic receptor complex 45 days postinfection. Therefore, these results suggest that the basis of verapamil's influence on the early critical period of infection is multifactorial and independent of a direct trypanocidal effect.

Gap junctions in vascular tissues. Evaluating the role of intercellular communication in the modulation of vasomotor tone

Integration and coordination of responses among vascular wall cells are critical to the local modulation of vasomotor tone and to the maintenance of circulatory homeostasis. This article reviews the vast literature concerning the principles that govern the initiation and propagation of vasoactive stimuli among vascular smooth muscle cells, which are nominally the final effectors of vasomotor tone. In light of the abundance of new information concerning the distribution and function of gap junctions between vascular wall cells throughout the vascular tree, particular attention is paid to this integral aspect of vascular physiology. Evidence is provided for the important contribution of intercellular communication to vascular function at all levels of the circulation, from the largest elastic artery to the terminal arterioles. The thesis of this review is that the presence of gap junctions, in concert with the autonomic nervous system, pacemaker cells, myogenic mechanisms, and/or electrotonic current spread (both hyperpolarizing and depolarizing waves through gap junctions), confers a plasticity, adaptability, and flexibility to vasculature that may well account for the observed diversity in regulation and function of vascular tissues throughout the vascular tree. It is hoped that the summary information provided here will serve as a launching pad for a new discourse on the mechanistic basis of the integrative regulation and function of vasculature, which painstakingly accounts for the undoubtedly complex and manifold role of gap junctions in vascular physiology/dysfunction.