Purinergic receptor-induced changes in paracellular resistance across cultures of human cervical cells are mediated by two distinct cytosolic calcium-related mechanisms

Research Progress in the Relationship Between P2X7R and Cervical Cancer

Cervical cancer is one of the most common and serious tumors in women. Finding new biomarkers and therapeutic targets plays an important role in the diagnosis, prognosis, and treatment of cervical cancer. Purinergic ligand-gated ion channel 7 receptor (P2X7R) is a purine ligand cation channel, activated by adenosine triphosphate (ATP). Studies have shown that P2X7R plays an important role in a variety of diseases and cancers. More and more studies have shown that P2X7R is also closely related to cervical cancer; therefore, the role of P2X7R in the development of cervical cancer deserves further discussion. The expression level of P2X7R in uterine epithelial cancer tissues was lower than that of the corresponding normal tissues. P2X7R plays an important role in the apoptotic process of cervical cancer through various mechanisms of action, and both antagonists and agonists of P2X7R can inhibit the proliferation of cervical cancer cells, while P2X7R is involved in the antitumor effect of Atr-I on cervical cancer cells. This review evaluates the current role of P2X7R in cervical cancer in order to develop more specific therapies for cervical cancer. In conclusion, P2X7R may become a biomarker for cervical cancer screening, and even a new target for clinical treatment of cervical cancer.

Purinergic signalling in epithelial ion transport: regulation of secretion and absorption

Intracellular ATP, the energy source for many reactions, is crucial for the activity of plasma membrane pumps and, thus, for the maintenance of transmembrane ion gradients. Nevertheless, ATP and other nucleotides/nucleosides are also extracellular molecules that regulate diverse cellular functions, including ion transport. In this review, I will first introduce the main components of the extracellular ATP signalling, which have become known as the purinergic signalling system. With more than 50 components or processes, just at cell membranes, it ranks as one of the most versatile signalling systems. This multitude of system components may enable differentiated regulation of diverse epithelial functions. As epithelia probably face the widest variety of potential ATP-releasing stimuli, a special attention will be given to stimuli and mechanisms of ATP release with a focus on exocytosis. Subsequently, I will consider membrane transport of major ions (Cl(-) , HCO(3)(-) , K(+) and Na(+) ) and integrate possible regulatory functions of P2Y2, P2Y4, P2Y6, P2Y11, P2X4, P2X7 and adenosine receptors in some selected epithelia at the cellular level. Some purinergic receptors have noteworthy roles. For example, many studies to date indicate that the P2Y2 receptor is one common denominator in regulating ion channels on both the luminal and basolateral membranes of both secretory and absorptive epithelia. In exocrine glands though, P2X4 and P2X7 receptors act as cation channels and, possibly, as co-regulators of secretion. On an organ level, both receptor types can exert physiological functions and together with other partners in the purinergic signalling, integrated models for epithelial secretion and absorption are emerging.

P2X(7) receptor expression is decreased in epithelial cancer cells of ectodermal, uro-genital sinus, and distal paramesonephric duct origin

The P2X(7) receptor is an important regulator of epithelial cell growth. The aim of the present study was to better understand the biological significance of P2X(7) receptor expression in normal and cancer human epithelial tissues. P2X(7) receptor and messenger RNA (mRNA) levels were determined in human tissues containing epithelial dysplastic, pre- or early cancerous, and cancer cells, and the levels were compared to those in the corresponding normal epithelial cells within the same tissue of the same case. P2X(7) receptor levels were determined by quantification of immunoreactivity specific to the functional (full-length) P2X(7) receptor, and P2X(7) mRNA levels were determined by real-time polymerase chain reaction. P2X(7) receptor levels in cancer cells were similar (colon adenocarcinoma) or greater (thyroid papillary carcinoma) than those in the corresponding normal cells. In contrast, in cancer cells of the ectocervix (squamous), endocervix and endometrium (adenocarcinoma), urinary bladder (transitional cell carcinoma), and breast (ductal and lobular adenocarcinomas), P2X(7) receptor levels were lower by about twofold than those in the corresponding normal epithelial cells. Similarly, P2X(7) mRNA levels were lower in uterine, bladder, and breast cancer epithelial tissues by about fourfold than those in the corresponding normal tissues. In addition, P2X(7) receptor levels were decreased already in dysplastic ectocervical cells and pre- or early cancerous endometrial and bladder cells. The data suggest that in epithelia originating from the ectoderm, the uro-genital sinus, and the distal paramesonephric duct, decreased expression of the P2X(7) receptor precedes or coincides with neoplastic changes in those tissues.

Estrogen modulation of MgATPase activity of nonmuscle myosin-II-B filaments

The study tested the hypothesis that estrogen controls epithelial paracellular resistance through modulation of myosin. The objective was to understand how estrogen modulates nonmuscle myosin-II-B (NMM-II-B), the main component of the cortical actomyosin in human epithelial cervical cells. Experiments used human cervical epithelial cells CaSki as a model, and end points were NMM-II-B phosphorylation, filamentation, and MgATPase activity. The results were as follows: 1) treatment with estrogen increased phosphorylation and MgATPase activity and decreased NMM-II-B filamentation; 2) estrogen effects could be blocked by antisense nucleotides for the estrogen receptor-alpha and by ICI-182,780, tamoxifen, and the casein kinase-II (CK2) inhibitor, 5,6-dichloro-1-beta-(D)-ribofuranosylbenzimidazole and attenuated by AG1478 and PD98059 (inhibitors of epithelial growth factor receptor and ERK/MAPK) but not staurosporine [blocker of protein kinase C (PKC)]; 3) treatments with the PKC activator sn-1,2-dioctanoyl diglyceride induced biphasic effect on NMM-II-B MgATPase activity: an increase at 1 nm to 1 microM and a decrease in activity at more than 1 microM; 4) sn-1,2-dioctanoyl diglyceride also decreased NMM-II-B filamentation in a monophasic and saturable dose dependence (EC(50) 1-10 microM); 5) when coincubated directly with purified NMM-II-B filaments, both CK2 and PKC decreased filamentation and increased MgATPase activity; 6) assays done on disassembled NMM-II-B filaments showed MgATPase activity in filaments obtained from estrogen-treated cells but not estrogen-depleted cells; and 7) incubations in vitro with CK2, but not PKC, facilitated MgATPase activity, even in disassembled NMM-II-B filaments. The results suggest that estrogen, in an effect mediated by estrogen receptor-alpha and CK2 and involving the epithelial growth factor receptor and ERK/MAPK cascades, increases NMM-II-B MgATPase activity independent of NMM-II-B filamentation status.

Changes in tight junctional resistance of the cervical epithelium are associated with modulation of content and phosphorylation of occludin 65-kilodalton and 50-kilodalton forms

Treatment of human cervical epithelial CaSki cells with ATP or with the diacylglyceride sn-1,2-dioctanoyl diglyceride (diC8) induced a staurosporine-sensitive transient increase, followed by a late decrease, in tight-junctional resistance (R(TJ)). CaSki cells express two immunoreactive forms of occludin, 65 and 50 kDa. Treatments with ATP and diC8 decreased the density of the 65-kDa form and increased the density of the 50-kDa form. ATP also decreased threonine phosphorylation of the 65-kDa form and increased threonine phosphorylation of the 50-kDa form and tyrosine phosphorylation of the 65- and 50-kDa forms. Staurosporine decreased acutely threonine and tyrosine phosphorylation of the two isoforms and in cells pretreated with staurosporine ATP increased acutely the density of the 65-kDa form and threonine phosphorylation of the 65-kDa form. Treatment with N-acetyl-leucinyl-leucinyl-norleucinal increased the densities of the 65- and 50-kDa forms. Pretreatment with N-acetyl-leucinyl-leucinyl-norleucinal attenuated the late decreases in R(TJ) induced by ATP and diC8 and the decrease in the 65-kDa and increase in the 50-kDa forms induced by ATP. Correlation analyses showed that high levels of R(TJ) correlated with the 65-kDa form, whereas low levels of R(TJ) correlated negatively with the 65-kDa form and positively with the 50-kDa form. The results suggest that in CaSki cells 1) occludin determines gating of the tight junctions, 2) changes in occludin phosphorylation status and composition regulate the R(TJ), 3) protein kinase-C-mediated, threonine dephosphorylation of the 65-kDa occludin form increases the resistance of assembled tight junctions, 4) the early stage of tight junction disassembly involves calpain-mediated breakdown of occludin 65-kDa form to the 50-kDa form, and 5) increased levels of the 50-kDa form interfere with occludin gating of the tight junctions.

Estrogen acidifies vaginal pH by up-regulation of proton secretion via the apical membrane of vaginal-ectocervical epithelial cells

The objective of this study was to assess estrogen-dependent cellular mechanisms that could contribute to the acid pH of the vaginal lumen. Cultures of normal human cervical-vaginal epithelial (hECE) cells and endocervical cells were grown on filters, and acidification of the extracellular solutions on the luminal (L-pHo) and contraluminal (CL-pHo) sides was measured. The hECE cells and endocervical cells decreased CL-pHo from 7.40 to 7.25 within 20-30 min of incubation in basic salt solution. Endocervical cells also produced a similar decrease in L-pHo. In contrast, hECE cells acidified L-pHo down to pH 7.05 when grown as monoculture and down to pH 6.05 when grown in coculture with human cervical fibroblasts. This enhanced acid secretion into the luminal compartment was estrogen dependent because removal of endogenous steroid hormones attenuated the effect, whereas treatment with 17beta-estradiol restored it. The 17beta-estradiol effect was dose dependent (EC50 0.5 nm) and could be mimicked by diethylstilbestrol and in part by estrone and tamoxifen. Preincubation with ICI-182780, but not with progesterone, blocked the estrogen effect. Preincubation of cells with the V-ATPase blocker bafilomycin A1, when administered to the luminal solution, attenuated the baseline and estrogen-dependent acid secretion into the luminal solution. Treatment with EGTA, to abrogate the tight junctional resistance, blocked the decrease in L-pHo and stimulated a decrease in CL-pHo, indicating that the tight junctions are necessary for maintaining luminal acidification. We conclude that vaginal-ectocervical cells acidify the luminal canal by a mechanism of active proton secretion, driven in part by V-H+-ATPase located in the apical plasma membrane and that the baseline active net proton secretion occurs constitutively throughout life and that this acidification is up-regulated by estrogen.

Antiapoptotic effects of estrogen in normal and cancer human cervical epithelial cells

The present study investigated the antiapoptotic effects of estrogen in normal and cancer human cervical cells and the mechanisms involved. Baseline apoptosis in human cervical epithelial cells is mediated predominantly by P2X7-receptor-induced, Ca(2+)-dependent activation of the mitochondrial (caspase-9) pathway. Treatment with 10 nM 17beta-estradiol blocked apoptosis induced by the P2X7-receptor ligands ATP and 2',3'-0-(4-benzoylbenzoyl)-ATP in normal human cervical epithelial cells (hECEs) and attenuated the effect in hECEs immortalized with human papillomavirus-16 (ECE16-1) and the cancer cervical cells HT3 and CaSki. Diethylstilbestrol and to a lesser degree estrone could mimic the effects of 17beta-estradiol, whereas actinomycin-D and cycloheximide attenuated the response. The antiapoptotic effect of estrogen did not depend on cell cycle phase, and in both normal and cancer cervical cells, it involved attenuation of activation of caspase-9 and the terminal caspase-3. However, involvement of cascades upstream to the caspase-9 differed in normal vs. cancer cervical cells. In the normal hECEs estrogen blocked P2X7-receptor-induced calcium influx. In contrast, in the cancer CaSki cells, estrogen up-regulated expression of Bcl-2 and attenuated Ca(2+)-induced mitochondrial swelling (i.e. formation of mitochondrial permeability transition pores). Estrogen had no effect on P2X7-receptor-induced apoptosis in the anaplastic SiHa and Hela cells. These results point to a novel antiapoptotic effect of estrogen in the cervix that is independent of its mitogenic function. The results also suggest that cancer cervical cells evolved antiapoptotic mechanisms that enable the cells to evade apoptosis and could therefore promote tumor progression.

P2X7 receptor-mediated apoptosis of human cervical epithelial cells

Normal human ectocervical epithelial (hECE) cells undergo apoptosis in culture. Baseline apoptosis could be increased by shifting cells to serum-free medium and blocked by lowering extracellular calcium. Treatment with the ATPase apyrase attenuated baseline apoptosis, suggesting that extracellular ATP and purinergic mechanisms control the apoptosis. Treatment with ATP and the P2X7 receptor analog 2'-3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP) increased apoptosis significantly, in a time- and dose-related manner. The threshold of ATP effect was 0.5 microM in hECE cells and approximately 1 microM in CaSki cancer cells. The apoptotic effect of BzATP was additive in part to that of tumor necrosis factor (TNF)-alpha, and it could be attenuated by lowering extracellular calcium and by treatment with the caspase-9 inhibitor Leu-Glu-His-Asp-O-methyl-fluoromethylketone (LEHD-FMK). Treatment with BzATP activated caspase-9, and, in contrast to TNF-alpha, it had only a mild effect on caspase-8. Both BzATP and TNF-alpha activated caspase-3, suggesting that BzATP activates predominantly the mitochondrial apoptotic pathway. Both hECE and CaSki cells secrete ATP into the extracellular fluid, and mean ATP activity in conditioned medium was approximately 0.5 microM, which is in the range of values that suffice to activate the P2X7 receptor. On the basis of these findings we propose a novel autocrine-paracrine mechanism of cervical cell apoptosis that operates by P2X7 receptor control of cytosolic calcium and utilizes the mitochondrial apoptotic pathway.

Expression, regulation, and function of P2X(4) purinergic receptor in human cervical epithelial cells

Micromolar concentrations of ATP stimulate biphasic change in transepithelial conductance across CaSki cultures on filters, an acute transient increase (phase I response; triggered by P2Y(2) receptor and mediated by calcium mobilization-dependent cell volume decrease) followed by a slower decrease in permeability (phase II response). Phase II response is mediated by augmented calcium influx and protein kinase C-dependent increase in tight junctional resistance. The objective of the study was to determine the role of P2X(4) receptor as a mediator of phase II response. Human cervical epithelial cells express P2X(4) receptor mRNA (1.4-, 2.2-, and 4.4-kb isoforms by Northern blot analysis) and P2X(4) protein. Depletion of vitamin A reversibly downregulated P2X(4) receptor mRNA and protein and ATP-induced calcium influx. Depletion of vitamin A abrogated phase II response, and the effect could be partially reversed only with retinoic acid receptor (RAR)-selective retinoids but not retinoid X receptor (RXR) agonists. Depletion of vitamin A also abrogated protein kinase C increase in tight junctional resistance, and the effect could not be reversed with retinoids. Depletion of vitamin A also abrogated phase I increase in permeability and reversibly downregulated P2Y(2) receptor mRNA and ATP-induced calcium mobilization. However, in contrast to phase II response, both RAR and RXR agonists could fully reverse those effects. These results suggest that phase II response is mediated by a P2X(4) receptor mechanism.

Regulation of transcervical permeability by two distinct P2 purinergic receptor mechanisms

Micromolar concentrations of ATP stimulate biphasic change in transepithelial conductance across CaSki cultures, an acute increase (phase I response) followed by a slower decrease (phase II response). Phase I and phase II responses involve two distinct calcium-dependent pathways, calcium mobilization and calcium influx. To test the hypothesis that phase I and phase II responses are mediated by distinct P2 purinergic receptors, changes in permeability were uncoupled by blocking calcium mobilization with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) or by lowering extracellular calcium, respectively. Under these conditions ATP EC(50) was 25 microM for phase I response and 2 microM for phase II response. The respective agonist profiles were ATP > UTP > adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma S) = N(6)-([6-aminohexyl]carbamoylmethyl)adenosine 5'-triphosphate (A8889) > GTP and UTP > ATP > GTP = A8889 > ATP-gamma S. Suramin blocked phase I response and ATP-induced calcium mobilization, whereas pyridoxal phosphate-6-azophenyl-2',4-disulfonic acid (PPADS) blocked phase II response and ATP-augmented calcium influx. ATP time course and pharmacological profiles for phase II response and augmented calcium influx were similar, with a time constant of 2 min and a saturable concentration-dependent effect (EC(50) of 2-3 microM). RT-PCR experiments revealed expression of mRNA for both the P2Y(2) and P2X(4) receptors. These results suggest that the ATP-induced phase I and phase II responses are mediated by distinct P2 purinergic receptor mechanisms.

Calcium regulates estrogen increase in permeability of cultured CaSki epithelium by eNOS-dependent mechanism

Estrogen increases baseline transepithelial permeability across CaSki cultures and augments the increase in permeability in response to hypertonic gradients. In estrogen-treated cells, lowering cytosolic calcium abrogated the hypertonicity-induced augmented increase in permeability and decreased baseline permeability to a greater degree than in estrogen-deprived cells. Steady-state levels of cytosolic calcium in estrogen-deprived cells were higher than in estrogen-treated cells. Increases in extracellular calcium increased cytosolic calcium more in estrogen-deprived cells than in estrogen-treated cells. However, in estrogen-treated cells, increasing cytosolic calcium was associated with greater increases in permeability in response to hypertonic gradients than in estrogen-deprived cells. Lowering cytosolic calcium blocked the estrogen-induced increase in nitric oxide (NO) release and in the in vitro conversion of L-[(3)H]arginine to L-[(3)H]citrulline. Treatment with estrogen upregulated mRNA of the NO synthase isoform endothelial nitric oxide synthase (eNOS). These results indicate that cytosolic calcium mediates the responses to estrogen and suggest that the estrogen increase in permeability and the augmented increase in permeability in response to hypertonicity involve an increase in NO synthesis by upregulation of the calcium-dependent eNOS.

Role of nitric oxide and cyclic guanosine 3',5'-monophosphate in the estrogen regulation of cervical epithelial permeability

Treatment of cultured human cervical epithelia on filters with 17beta-estradiol increases paracellular permeability in a time- and dose-related manner (EC50, 1.1 nM). The objective of the present study was to understand the molecular mechanisms of estrogen action. In cultured human cervical epithelial cells the nitric oxide (NO) donors sodium nitroprusside (SNP) and N-[ethoxycarbonyl]-3-[4-morpholinyl]sydnoneimine (SIN-I) and the cell-permeable cGMP analog 8-bromo-cGMP (8-Br-cGMP) increased paracellular permeability. In estrogen-treated cells SNP and 8-Br-cGMP increased permeability to a lesser degree than in estrogen-deprived cells, suggesting that NO and cGMP mediate the effect of estrogen on permeability. Tamoxifen blocked the estrogen-induced increase in permeability, but it had no effect on increases in permeability that were induced by SNP or by 8-Br-cGMP. LY-83583 (blocker of guanylate cyclase) attenuated the effect of SNP, whereas KT-5823 (blocker of cGMP-dependent protein kinase) abrogated the effects of both SNP and 8-Br-cGMP. Treatment with 17beta-estradiol increased NO release and cellular cGMP in a dose-related manner (EC50, approximately 1 nM), and the effects were inhibited by tamoxifen. Treatment with SNP increased cGMP maximally, even in estrogen-deficient cells. LY-83583 blocked the estrogen-induced increase in cGMP, but neither LY-83583 nor KT-5823 had a significant effect on the estrogen-induced increases in NO release and cellular cGMP. The NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester decreased NO release, and pretreatment of cells with L-arginine reversed the effect. Cultured human cervical epithelial cells express messenger RNA for the NOS isoforms endothelial NOS (ecNOS), brain NOS, and inducible NOS. 17beta-Estradiol up-regulated ecNOS messenger RNA, and tamoxifen blocked the effect. Based on these results we suggest that the effect of estradiol on permeability involves four signaling steps: 1) activation of estrogen receptors, 2) increase in ecNOS transcription and up-regulation of NO activity, 3) NO activation of guanylate cyclase and increase in cGMP, and 4) cGMP activation of cGMP-dependent protein kinase.

NO increases permeability of cultured human cervical epithelia by cGMP-mediated increase in G-actin

Human cervical epithelial cells express mRNA for the nitric oxide (NO) synthase (NOS) isoforms ecNOS, bNOS, and iNOS and release NO into the extracellular medium. N(G)-nitro-L-arginine methyl ester (L-NAME), an NOS inhibitor, and Hb, an NO scavenger, decreased paracellular permeability; in contrast, the NO donors sodium nitroprusside (SNP) and N-(ethoxycarbonyl)-3-(4-morpholinyl)sydnonimine increased paracellular permeability across cultured human cervical epithelia on filters, suggesting that NO increases cervical paracellular permeability. The objective of the study was to understand the mechanisms of NO action on cervical paracellular permeability. 8-Bromo-cGMP (8-BrcGMP) also increased permeability, and the effect was blocked by KT-5823 (a blocker of cGMP-dependent protein kinase), but not by LY-83583 (a blocker of guanylate cyclase). In contrast, LY-83583 and KT-5823 blocked the SNP-induced increase in permeability. Treatment with SNP increased cellular cGMP, and the effect was blocked by Hb and LY-83583, but not by KT-5823. Neither SNP nor 8-BrcGMP had modulated cervical cation selectivity. In contrast, both agents increased fluorescence from fura 2-loaded cells in the Ca(2+)-insensitive wavelengths, indicating that SNP and 8-BrcGMP stimulate a decrease in cell size and in the resistance of the lateral intercellular space. Neither SNP nor 8-BrcGMP had an effect on total cellular actin, but both agents increased the fraction of G-actin. Hb blocked the SNP-induced increase in G-actin, and KT-5823 blocked the 8-BrcGMP-induced increase in G-actin. On the basis of these results, it is suggested that NO acts on guanylate cyclase and stimulates an increase in cGMP; cGMP, acting via cGMP-dependent protein kinase, shifts actin steady-state toward G-actin; this fragments the cytoskeleton and renders cells more sensitive to decreases in cell size and resistance of the lateral intercellular space and, hence, to increases in permeability. These results may be important for understanding NO regulation of transcervical paracellular permeability and secretion of cervical mucus in the woman.

A novel fluorescence chamber for the determination of volume changes in human CaSki cell cultures attached on filters

The objective of the study was to test the hypothesis that, in the cultured human cervical epithelium, CaSki, the effect of calcium mobilizing agents on transepithelial electrical conductance (GTE), is the result of cell volume decrease. CaSki cells attached on filters were loaded with fura-2, and measurements of fluorescence at the isosbestic wavelength 360 nm (excitation/emission [F360/510]) were made in a newly designed fluorescence chamber; this design allowed us also to determine changes in cytosolic calcium ([Ca2+]i). The experimental conditions were similar to those used to measure changes in paracellular permeability in the Ussing chamber, and they enabled us to compare the time-course of changes in [Ca2+]i, in F360/510, and in GTE. Hypertonicity increased, and hypotonicity decreased F360/510 and GTE, without having an effect on [Ca2+]i, and the changes in F360/510 and in GTE correlated linearly. Metabolism, bleaching, and extrusion of intracellular fura-2 were minimal, indicating that the changes in F360/510 reflect changes in dye concentration. Hypertonicity decreased, and hypotonicity increased the size of dispersed CaSki cells, suggesting that osmolarity-induced changes in F360/510 reflect changes in size of the attached cells. Ionomycin increased [Ca2+]i, F360/510, and GTE, but the increases in [Ca2+]i preceded those in F360/510 and GTE. The calcium chelator BAPTA blocked the ionomycin-induced increase in [Ca2+]i, F360/510, and in GTE. Preincubation with 4-acetamido-4'isothiocyanatostilbene-2,2'disulfonic acid (SITS) augmented the ionomycin-induced increase in [Ca2+]i, but blocked the increases in F360/510 and in GTE. Pretreatment of cells with hypertonic solution abrogated the increases in F360/510 and in GTE in response to ionomycin, but had little effect on the ionomycin-induced increase in [Ca2+]i. On the basis of these results we suggest that the ionomycin-induced increase in GTE is mediated by [Ca2+]i-dependent chloride secretion and osmotic water loss.

Seminal fluid factor increases the resistance of the tight junctional complex of cultured human cervical epithelium CaSki cells

OBJECTIVE

To determine the effects of human seminal fluid on cervical paracellular resistance.

DESIGN

Experimental study.

SETTING

Healthy volunteers in an academic research environment; cultures of human CaSki cells on filters, with phenotypic characteristics of the endocervix.

PATIENT(S)

Healthy men donating sperm to a sperm bank.

INTERVENTION(S)

Seminal fluid was obtained as the discarded fluid from ejaculates.

MAIN OUTCOME MEASURE(S)

Changes in transepithelial electrical resistance across CaSki cells on filters were determined in an Ussing chamber from successive measurements of the short-circuit current and the transepithelial potential difference. Changes in the dilution potential (and hence in the ratio of Cl- to Na+ mobilities) were determined after lowering the NaCl concentration in the luminal solution.

RESULT(S)

Seminal fluid increased transepithelial electrical resistance acutely (t1/2, 2 minutes), reversibly, and in a dose-related manner (ED50, 1%). The effect of seminal fluid was abolished when the extracellular calcium level was lowered, and the increase in transepithelial electrical resistance correlated with a decrease in the ratio Cl- to Na+ mobilities, indicating an increase in the resistance of the tight junctional complex. The increase in transepithelial electrical resistance in response to seminal fluid was nonadditive to that of sn-1,2-dioctanoyl diglyceride (a stable diacylglyceride and activator of protein kinase C), and it was abolished by prolonged preincubation with the phorbol ester phorbol 12-myristate 13-acetate (to downregulate protein kinase C) or with staurosporin (to inhibit protein kinase C), suggesting that seminal fluid acts through a protein kinase C-dependent mechanism. Slower (t1/2, 3.3 minutes) increases in transepithelial electrical resistance occurred when seminal fluid was added only to the luminal or the subluminal solution. Treatment with pertussis toxin, adenosine triphosphatase, or trypsin had no effect on the changes in transepithelial electrical resistance. Seminal fluid increased cytosolic calcium, but changes in cytosolic calcium are not important for the increases in transepithelial electrical resistance, suggesting that the effect of seminal fluid is not receptor-mediated. Preliminary studies indicate that the factor(s) in seminal fluid that increases transepithelial electrical resistance is a labile, low molecular weight (< 10 kd) lipid.

CONCLUSION(S)

Seminal fluid may regulate cervical mucus production in vivo by modulating endocervical permeability.