Angiotensin II activation of protein kinase C decreases delayed rectifier K+ current in rabbit vascular myocytes

1. The effect of angiotension II (Ang) on delayed rectifier K+ current (IK(V)) was studied in isolated rabbit portal vein smooth muscle cells using standard whole-cell voltage clamp technique. The effect of 100 nM Ang on macroscopic, whole-cell IK(V) was assessed in myocytes dialysed with 10 mM BAPTA, 5 mM ATP and 1 mM GTP either at room temperature or at 30 degrees C. 2. Application of Ang caused a decline in IK(V) which was reversed upon washout of the drug. Tail current recorded after 250 ms pulses to +30 mV and repolarization to -40 mV was reduced from 3.9 +/- 0.7 to 2.5 +/- 0.5 pA pF-1 at 20 degrees C (n = 6) and from 4.5 +/- 0.5 to 3.13 +/- 0.4 pA pF-1 at 30 degrees C(n = 17). 3. Ang had no effect on outward current in the presence of an AT1 selective antagonist, losartan (1 microM), which alone had no direct effect on the amplitude of IK(V). Substitution of extracellular Ca2+ with Mg2+ in the presence of 10 microM intracellular BAPTA did not affect the suppression of IK(V) by Ang. 4. Ang induced a decrease in time constant for the rapid phase of inactivation of the macroscopic current (tau 1 reduced from 377 +/- 32 to 245 +/- 11 ms; tau 2 unchanged, n = 17). Neither the voltage dependence of activation nor inactivation were affected by Ang. 5. The inhibition of IK(V) by Ang was abolished by intracellular dialysis with the selective PKC inhibitors, calphostin C (1 microM) and chelerythrine (50 microM). These data provide strong evidence that the decline in IK(V) due to Ang treatment is due to PKC activation. 6. The pattern of expression of PKC isoforms was examined in rabbit portal vein using isoenzyme-specific antibodies: alpha, epsilon and zeta isoenzymes were detected, but beta, gamma, delta and eta isoenzymes were not. 7. The lack of requirement for Ca2+, as well as the sensitivity of the Ang response to chelerythrine, suggest the involvement of the Ca(2+)-independent PKC isoenzyme epsilon in the signal transduction pathway responsible for IK(V) inhibition by Ang.

Block of large conductance Ca(2+)-activated K+ channels in rabbit vascular myocytes by internal Mg2+ and Na+

1. We studied the biophysical properties of single large conductance (> 200 pS in symmetrical K+ pipette and bath solutions) Ca(2+)-activated K+ (BKca) channels of rabbit portal vein and coronary arterial smooth muscle cells using the cell-attached and inside-out variants of the patch-clamp technique (at 22 degrees C). 2. The unitary conductance of BKca channels recorded in cell-attached patches with K+ concentrations in the range 5.4-140 mM was significantly lower than that predicted on the basis of the conductance measured in inside-out patches with symmetrical K+ pipette and bath solutions (140 mM) and the constant field equation. In cell-attached patches from cells bathed in depolarizing medium (140 mM) with 5.4 mM K+ in the pipette solution, BKca channels were difficult to detect on the physiological range of membrane potentials (approximately -50 mV). Unitary currents were smaller at all voltages in the range -50 to 0 mV and the i-V relationship exhibited strong inward rectification at potentials > 0 mV. These channels were unequivocally identified as BKca channels due to their sensitivity to caffeine (10 mM) and iberiotoxin (20 nM), and their non-stationary kinetic properties. 3. Exposure of the cytoplasmic side of excised patches to [Mg2+] in the range 0-15 mM produced two effects on BKca channel activity: the slope conductance and open probability were reduced and enhanced, respectively, in a concentration-dependent manner by this cation. The Mg(2+)-induced reduction in conductance exhibited weak voltage dependence. 4. Application of 20 mM Na+ to the internal face of BKca channels recorded in the inside-out configuration produced a flickery block at potentials > or = +20 mV resulting in reduced unitary current amplitudes and strong inward rectification of the i-V relationship. Exposure of inside-out patches to a combination of 20 mM Na+ and 2 mM Mg2+ further reduced unitary current amplitude to a level similar to the algebraic sum of the effect of each cation in isolation. 5. We conclude that Ca(2+)-dependent K+ channels of vascular smooth muscle cells display a lower unitary conductance when recorded under physiological conditions than that previously estimated on the basis of their behaviour in excised membrane patches. Our data indicate that the decreased permeation through BKca channels may be partly attributed to block by intracellular Mg2+ and Na+, which appear to interact with distinct binding sites along the inner side of the pore.

Regulation of 4-aminopyridine-sensitive, delayed rectifier K+ channels in vascular smooth muscle by phosphorylation

Voltage-gated, delayed rectifier K+ current (KV) that is sensitive to 4-aminopyridine (4AP) block has been identified in all vascular smooth muscle tissues studied to date. These channels conduct outward, hyperpolarizing K+ current that influences resting membrane potential and contributes to repolarization of action potentials. Smooth muscle cells in most arterial resistance vessels regulate Ca2+ influx and contractile tone by low amplitude, tonic changes in membrane potential. Block of KV with 4-aminopyridine leads to contraction and an enhanced myogenic response to increased intravascular pressure. We investigated the modulation of KV currents in isolated, freshly dispersed smooth muscle cells from rabbit portal vein and coronary arteries in whole-cell voltage clamp experiments. Our findings indicate that KV channels are regulated by signal transduction mechanisms involving vasoactive agonists that activate cAMP-dependent protein kinase (PKA) or protein kinase C (PKC). In this paper, the properties and potential function of KV channels in vascular smooth muscle are reviewed. Further, the regulation and potential role of alterations in KV due to beta-adrenoceptor agonists, adenylyl cyclase and PKA, as well as angiotensin II, diacylglycerol, and PKC are discussed.

Protein kinase C inhibits delayed rectifier K+ current in rabbit vascular smooth muscle cells

The effect of protein kinase C (PKC) activation on 4-aminopyridine (4-AP)-sensitive delayed rectifier current (IdK) was studied in isolated rabbit portal vein smooth muscle cells by use of standard whole cell voltage clamp. The effects of the phorbol ester, 4 beta-phorbol 12,13-dibutyrate (PdBu, 100 nM) and diacylglycerol analogues, 1,2-dioctanoyl-sn-glycerol (1,2-diC8, 10 microM) and 1,3-dioctanoyl-sn-glycerol (1,3-diC8, 10 microM), on macroscopic whole cell IdK were assessed in myocytes dialyzed with 10 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) and 5 mM ATP (20-22 degrees C). Activation of PKC by 1,2-diC8 or PdBu caused a decline in IdK that was reversed with washout of drug. 1,2-diC8 had no effect on outward current present after exposure to 4-AP (20 mM). The inactive analogue, 1,3-diC8, did not affect IdK, but subsequent exposure to the active analogue, 1,2-diC8, caused a marked depression of the current. The inhibition of IdK by 1,2-diC8 was significantly reduced by intracellular dialysis with the inhibitors of PKC, chelerythrine (50 microM) and calphostin C (1 microM). Substitution of extracellular Ca2+ with Mg2+ in the presence of 10 mM intracellular BAPTA did not affect the suppression of IdK by 1,2-diC8, indicating the involvement of a Ca(2+)-independent isoform of PKC. This study suggests a novel signal transduction mechanism for inhibition of 4-AP-sensitive IdK involving a phosphotransferase reaction catalyzed by PKC in vascular smooth muscle myocytes.

Endothelium-dependent hyperpolarization of vascular smooth muscle: role for a non-nitric oxide synthase product

There is now a considerable evidence that indicates that there is non-NO/prostanoid mediated vasodilation/hyperpolarization mechanism in a variety of blood vessels from different species. It is argued that a factor, EDHF, is responsible for mediating these cellular events and, like NO, EDHF is synthesized and released, in a Ca(2+)-dependent manner, from endothelial cells and activates vascular K+ channel(s) with the predominant evidence suggesting K(Ca) (iberiotoxin and/or apamin sensitive) though this remains to be absolutely confirmed. A number of studies also indicate that a cytochrome P-450 metabolite of arachidonic acid, namely an epoxyeicosatrienoic acid, may serve as the chemical messenger between endothelial and vascular smooth muscle cells. Evidence confirming that there is chemical transmission between endothelial and vascular smooth muscle cells is, however, minimal. Although significant progress has been recently made, much needs to be discovered concerning the nature, synthesis, release, vascular effects as well as the role of EDHF in normal and diseased vascular tissue.

Arrhythmia and delayed recovery of cardiac action potential during reperfusion after ischemia. Role of oxygen radical-induced no-reflow phenomenon

The role of reactive metabolites of oxygen, oxygen radicals (O-Rs), as mediators of potentially arrhythmogenic alterations in cellular electrical properties and contractile dysfunction of cardiac muscle during reperfusion after ischemia was investigated. Electrical and mechanical activities of arterially perfused guinea pig right ventricular walls were recorded simultaneously with intracellular microelectrodes and a force transducer. Preparations were maintained in Krebs-Henseleit solution (perfusion rate, 1.5 mL/min) and subjected to 30 minutes of no-flow ischemia followed by 60 minutes of reperfusion or pretreated with O-R scavengers (superoxide dismutase, 50 U/mL; catalase, 600 U/mL; and mannitol, 2 mmol/L) for 10 to 20 minutes, followed by 30 minutes of ischemia and 60 minutes of reperfusion. Reperfusion in untreated preparations caused (1) depolarization of resting membrane potential by 8 to 10 mV and slow recovery of action potential duration requiring 60 minutes to attain the preischemic duration, (2) tachyarrhythmias and premature action potentials, (3) postischemic contractile dysfunction, and (4) increased coronary perfusion pressure in untreated preparations. Pretreatment with scavenger cocktail affected neither electrical nor contractile activity before or during no-flow ischemia, but it (1) accelerated recovery of resting membrane potential and action potential duration, (2) reduced the incidence of tachyarrhythmia, (3) improved contractile function, and (4) inhibited the rise in perfusion pressure on reflow. Reperfusion with an exogenous O-R-generating system containing xanthine/xanthine oxidase (X/XO, 2 mmol/L:10 mU/mL) inhibited recovery of action potential duration and contractility. Treatment of normoxic arterially perfused right ventricular walls with X/XO caused a decline in action potential duration by approximately 20% within 30 minutes. In contrast, X/XO caused a 30% increase in the duration of action potentials in superfused papillary muscles or small strips of right ventricular walls over the same time period. Pretreatment with sodium nitroprusside (10 mumol/L) inhibited the decline in duration induced by X/XO in normoxic right ventricular walls but was without effect on prolongation due to X/XO in papillary muscles. Reperfusion with nitroprusside after no-flow ischemia caused (1) accelerated recovery of preischemic action potential configuration, (2) a significant decline in the incidence of reperfusion arrhythmias, (3) improved postischemic contractile performance, and (4) inhibition of the increase in perfusion pressure associated with reflow. The data indicate that slow recovery of the action potential duration caused by O-Rs in reperfusion cannot be explained by the direct effects of O-Rs on cardiac myocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Oxygen-derived free radical stress activates nonselective cation current in guinea pig ventricular myocytes. Role of sulfhydryl groups

Oxygen-derived free radicals (O-Rs) cause alterations in cardiac electrical activity, including sustained depolarization, which may contribute to arrhythmic activity in reperfusion after ischemia. The ionic current(s) and cellular mechanism(s) underlying the sustained depolarization are not well defined. We used the whole-cell variant of the patch-clamp technique to study sustained depolarization in guinea pig ventricular myocytes during the extracellular application of O-Rs (generating system: dihydroxyfumaric acid, 3 to 6 mmol/L; FeCl3/ADP, 0.05:0.5 mmol/L). Myocytes superfused with O-Rs (pipette EGTA, 0.1 mmol/L) showed (1) sustained depolarization to between -40 and -10 mV, (2) oscillations in membrane potential, and (3) triggered activity. The depolarization resulted from an increase in quasi-steady state difference current reversing at approximately -18 mV, and the oscillations were due to transient inward current. The latter were inhibited with ryanodine (10 mumol/L) or high pipette EGTA (5 mmol/L), but the steady state current was unaffected. Nonselective cation current (INSC) (recorded with Cs+, Li+, and Mg2+ replacing K+, Na+, and Ca2+, respectively; 20 mmol/L tetraethylammonium chloride [TEA] and 5 mmol/L BAPTA in the pipette solution and 10 mmol/L TEA, 10 mumol/L tetrodotoxin, and 10 mumol/L nicardipine in the bath solution) was activated by O-Rs; the increase in current was unaffected by preventing changes in [Ca2+]i but was inhibited with dithiothreitol. Oxidizing agents (diamide and thimerosal) or caffeine (pipette EGTA, 0.1 mmol/L) produced a similar increase in membrane conductance. INSC activated with O-Rs, oxidizing agents, or caffeine was sensitive to SK&F 96365. O-R treatment was without effect when INSC was already activated with caffeine. The data suggest that (1) extracellular O-Rs activate a Ca(2+)-sensitive INSC in the absence of changes in [Ca2+]i, (2) oxidative modification of extracellular sulfhydryl groups may be involved, and (3) this mechanism is different from the Ca(2+)-dependent activation of INSC by intracellular O-Rs, indicating that O-Rs may alter ion channel activity by differential mechanisms, depending on the compartment, extracellular or intracellular, in which they are present.

Phosphorylation by protein kinase A enhances delayed rectifier K+ current in rabbit vascular smooth muscle cells

The effect of adenosine 3',5'-cyclic monophosphate-dependent protein kinase (PKA) activity on 4-aminopyridine (4-AP)-sensitive delayed rectifier current (IdK) in isolated rabbit portal vein smooth muscle cells was studied via whole cell voltage clamp (20-22 degrees C). A threefold increase in 4-AP-sensitive (5 mM) IdK was recorded after gaining cell access during dialysis with 5 mM intracellular ATP and internal Ca2+ buffered to a low level with 5 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. Dialysis with the nonhydrolyzable ATP analogue 5'-adenylylimidodiphosphate (5 mM) or the specific peptide inhibitor of PKA (PKI; 10 microM) reduced current runup by 50 and 70%, respectively. Delayed dialysis with PKI reversed runup and inhibited IdK to below initial levels. Forskolin (1 microM) caused a reversible increase in IdK, which was inhibited by 4-AP (5 mM). Isoproterenol (1 microM) reversibly enhanced IdK; the increase was sensitive to propranolol (2 microM) and 4-AP (5 mM) and was prevented by dialysis with PKI (10 microM). IdK was enhanced over the entire voltage range of activation and associated with a negative shift in reversal potential of net whole cell current, consistent with hyperpolarization of resting membrane potential. The data provide the first evidence for a signal transduction mechanism involving beta-adrenoceptors, adenylate cyclase, and a phosphotransferase reaction mediated by PKA for the regulation of delayed rectifier K+ channels in vascular smooth muscle.

Metabolic inhibition enhances Ca(2+)-activated K+ current in smooth muscle cells of rabbit portal vein

The effect of metabolic inhibition on macroscopic and single-channel K+ currents in isolated rabbit portal vein myocytes was investigated by patch-clamp technique. Depression of adenosine triphosphate synthesis was produced by 2-deoxy-D-glucose (10 mM) and either cyanide (2 mM) or dinitrophenol (50 microM). Outward quasi-steady-state current evoked by a ramp protocol and outward time-dependent current during step depolarizations were increased during metabolic inhibition. The reversal potential for quasi-steady-state current shifted negatively toward equilibrium potential of K+ during treatment consistent with a role for K+ conductance and hyperpolarization of membrane potential. The macroscopic K+ current affected was 1) voltage dependent, 2) inhibited by intracellular Ca2+ chelation and low tetraethylammonium ion (1 mM) but unaffected by 4-aminopyridine (2 mM), and 3) associated with a rise in intracellular Ca2+ assessed by indo 1. Metabolic inhibition caused an increase in voltage-dependent large-conductance K+ channel (120-130 pS) activity in cell-attached patches of myocytes bathed in physiological solution (140 mM K+ in pipette). The channels were blocked in a flickery fashion by tetraethylammonium ion (0.5 mM) and inhibited with charybdotoxin (100 nM). We conclude that metabolic inhibition increases the activity of large-conductance Ca(2+)-activated K+ channels in vascular smooth muscle.

Ischemic cardioprotection by ATP-sensitive K+ channels involves high-energy phosphate preservation

We previously demonstrated that ATP-sensitive K+ channels (KATP) protect the guinea pig myocardium against ischemia-reperfusion injury (Cole et al., Circ. Res. 69: 571-581, 1991), but the cellular alterations leading to ischemic injury affected by KATP remain to be defined. This study investigates the relationship between activation of KATP and preservation of high-energy phosphates during global no-flow ischemia in arterially perfused guinea pig right ventricular walls. Electrical and mechanical activity were recorded via intracellular microelectrodes and a force transducer. Glibenclamide (10 and 50 microM) and pinacidil (10 microM) were used to modulate KATP. ATP and creatine phosphate (CP) levels were determined at the end of no-flow ischemia by enzymatic analysis. Preparations were subjected to 1) 20 min no-flow +/- glibenclamide (10 or 50 microM), 2) 30 min no-flow +/- pinacidil (10 microM) or pinacidil (10 microM) and glibenclamide (50 microM), or 3) 40 or 50 min of control perfusion before rapid freezing in liquid nitrogen. Pinacidil (10 microM) enhanced ischemic shortening of action potential duration (APD) and early contractile failure, prevented ischemic contracture, and inhibited high-energy phosphate depletion during ischemia. Glibenclamide (50 microM) inhibited the effects of pinacidil (10 microM) on electromechanical function and preservation of ATP and CP. Glibenclamide (10 microM) alone inhibited the early decline in APD and produced earlier ischemic contracture but did not enhance ATP or CP depletion compared with untreated tissues during 20 min of no-flow. Glibenclamide (50 microM) produced a greater inhibition of APD shortening in early ischemia, further decreased the latency to ischemic contracture, and caused enhanced ischemic depletion of ATP. The data indicate the changes in electrical activity induced by KATP indirectly preserve high-energy phosphates and reduce injury associated with ischemia. However, the data also suggest the possible presence of additional mechanisms for cardioprotection by KATP.

ATP-sensitive K+ channels in cardiac ischemia: an endogenous mechanism for protection of the heart

The Role of ATP-sensitive K+ channels (KATP) in action potential shortening and protection of myocardium in ischemia were explored using isolated ventricular myocytes and arterially perfused right ventricular walls of guinea pigs. Conditions "simulating" some aspects of ischemia--(10.8 mM K+o, 6.9 pHo, 20 mM lactate, no glucose; 10 mM 2-deoxy-D-glucose; and either 1 mM cyanide or no O2 (bubbled with 95/5% N2/CO2)--caused a decline in action potential duration (APD) and the elaboration of time- and voltage-independent, steady-state outward conductance due to KATP, which could be inhibited with glibenclamide (50 microM) in myocytes studied via the perforated patch (nystatin) whole-cell technique. Right ventricular walls subjected to no-flow ischemia +/- glibenclamide (10 microM) to block, or +/- pinacidil (1 and 10 microM) to activate, KATP, respectively, exhibited varied ischemic injury. Glibenclamide caused a greater fall in resting membrane potential, inhibited the decline in APD, caused an early rise in resting tension, and inhibited recovery of contractile function upon reflow. Pinacidil caused a greater decline in APD, inhibited changes in resting tension, and improved recovery during reperfusion. These results indicate that KATP contributes to action potential shortening in isolated myocytes in simulated ischemia and intact myocardium in no-flow ischemia. Activation of this membrane current may be an important adaptive mechanism for protecting the myocardium when blood flow to the tissue is compromised.

Chloramine-T induced binding of monoclonal antibody B72.3 to concanavalin-A

The effects of chloramine-T (CT) on monoclonal antibody B72.3 were studied with particular reference to Con-A lectin binding. After exposure to chloramine-T concentrations from 0.8 to 4.0 mg/mL (115-574 mol CT/mol B72.3), B.72.3 showed progressive binding to agarose-linked Con-A. This behavior was paralleled by decreasing immunoreactivity and increasing fragmentation and aggregation of B72.3 demonstrated by SDS-PAGE and size exclusion HPLC.

Modulation of cardiac performance by amiloride and several selected derivatives of amiloride

Amiloride and its derivatives (benzamil, dichlorobenzamil, 5-(N,N-dimethyl)-amiloride, 5-(N-ethyl-N-isopropyl)-amiloride, (N,N-hexamethylene)- amiloride and 5-(N-methyl-N-isobutyl)-amiloride) are commonly used as selective blockers of Na+/Ca++ exchange or Na+/H+ exchange. Very little information is currently available regarding their effects on cardiac performance. It was observed that addition of amiloride or any of the selected derivatives to the coronary perfusate of the right ventricular wall produced a potent depressive effect on peak developed tension and the rates of tension generation and dissipation. The concentrations at which this occurred are those that are commonly used in ischemia or hypoxia studies. Significantly, the depressive action of the drugs increased with the perfusion duration and never achieved a stable level. An initial, transient positive inotropic effect was observed with some of the drugs. If the drug concentration and perfusion time was limited, the effects were reversible. All of the drugs except amiloride produced extra systoles. The drugs were capable of blocking Ca++ transients in isolated cardiomyocytes but had little effect on intracellular pH. The drugs lengthened the action potential duration and decreased the action potential amplitude and upstroke velocity. Their effects on cardiac performance may involve a complex inhibition of Ca++ influx and K+ efflux in addition to a stimulation of a nonselective cation current. It is concluded that amiloride and its analogs have striking effects on cardiac performance which may be unrelated to their capacity to inhibit Na+/Ca++ or Na+/H+ exchange. In summary, the use of these drugs is not normally recommended in cell or tissue perfusion experiments because of their nonselectivity. However, if the drug concentration and perfusion time is controlled carefully, interpretable data may be obtained in some cases.

Alterations in electrical activity and membrane currents induced by intracellular oxygen-derived free radical stress in guinea pig ventricular myocytes

Oxygen-derived free radicals (O-Rs) are thought to induce alterations in cardiac electrical activity; however, the underlying membrane ionic currents affected by O-Rs and the mechanisms by which O-Rs induce their effects on ion channels in the heart are not well defined. In this study, we investigated the time-dependent changes in resting membrane potential and action potential configuration and changes in steady-state membrane currents in guinea pig ventricular myocytes after intracellular application of an O-R-generating system. O-Rs were generated from the combination of dihydroxyfumaric acid (3 mM) and FeCl3:ADP (0.05:0.5 mM) added to the pipette solution that was used to record membrane potential and currents via the whole-cell variant of the patch-clamp technique. Intracellular exposure of myocytes to the O-R-generating solution induced three stages of changes: 1) an early depolarization (5-10 mV) and an increase in action potential duration accompanied by a decrease in resting inward rectifying K+ current conductance, 2) delayed afterdepolarizations and triggered activity caused by the activation of transient inward current mediated by Na(+)-Ca2+ exchange, with failure to repolarize and sustained depolarization between -35 and -20 mV, reflecting the stimulation of nonselective cation current, and 3) a late stage of marked decline in action potential duration, hyperpolarization, and loss of excitability accompanied by activation of the outward current through ATP-sensitive K+ channels. These alterations in electrical activity and membrane currents could be prevented by pretreatment with N-(2-mercaptopropionyl)glycine (500 microM), a scavenger of hydroxyl free radicals. The alterations associated with stages 1 and 2 but not stage 3 were completely abolished on intracellular Ca2+ chelation (5 mM EGTA in the pipette solution) or disruption of sarcoplasmic reticulum Ca2+ handling with ryanodine (10 microM). This study shows that intracellular O-R stress causes specific alterations in membrane ionic currents, leading to changes in resting membrane potential and action potential configuration. Moreover, the data indicate that an elevation in intracellular Ca2+ due to abnormal Ca2+ handling by the sarcoplasmic reticulum is a cause of some of the alterations in membrane currents during O-R stress.

The origin of biexponential T2 relaxation in muscle water

Two theories have been proposed to explain the multiexponential transverse relaxation of muscle water protons: "anatomical" and "chemical" compartmentation. In an attempt to obtain evidence to support one or the other of these two theories, interstitial and intracellular macromolecular preparations were studied and compared with rat muscle tissue by proton NMR transverse relaxation (T2) measurements. All macromolecule preparations displayed monoexponential T2 decay. Membrane alteration with DMSO/glycerin did not eliminate the biexponential T2 decay of muscle tissue. Maceration converted biexponential T2 decay of muscle tissue to single exponential decay. It is concluded that the observed two component exponential T2 decay of muscle represents anatomical compartmentation of tissue water, probably intracellular versus extracellular.

ATP-regulated K+ channels protect the myocardium against ischemia/reperfusion damage

The role of ATP-regulated K+ channels in protecting the myocardium against ischemia/reperfusion damage was explored using glibenclamide and pinacidil to block and activate the channels, respectively. Electrical and mechanical activity of arterially perfused guinea pig right ventricular walls was recorded simultaneously via an intracellular microelectrode and a force transducer. The preparations were subjected to either 1) 20 minutes of no-flow ischemia with or without glibenclamide (1 and 10 microM) followed by reperfusion, or 2) 30 minutes of no-flow ischemia with or without pinacidil (1 and 10 microM) followed by reperfusion. No-flow ischemia for 20 minutes produced changes in electrical and mechanical activity that were completely reversed on reperfusion; resting membrane potential declined by 13 +/- 1.2 mV, action potential duration at 90% repolarization (APD90) decreased by 62%, and developed tension fell by greater than 95%, but resting tension did not change significantly. Glibenclamide (10 microM) had no effect on activity during normal perfusion, but during ischemia, resting membrane potential fell slightly further (17 +/- 1.8 mV) and APD90 declined by only 24%. Developed tension declined more slowly and to a lesser extent, but resting tension rose significantly between 10 and 20 minutes of ischemia. Reperfusion of glibenclamide-treated tissues elicited arrhythmias (extrasystoles and tachycardia), and the preparations failed to recover mechanical function. Glibenclamide at 1 microM produced qualitatively similar effects, albeit less severe. After 30 minutes of no-flow ischemia in untreated tissues, resting tension increased by approximately 130% during the no-flow period. Reperfusion caused arrhythmias (extrasystoles, tachyarrhythmias, and fibrillation) and failed to restore resting or developed tension to preischemic levels. Pinacidil at 1 microM did not affect electrical or contractile function, but at 10 microM it had a negative inotropic effect, decreasing APD90 and developed tension by 5% and 18%, respectively. Both concentrations of the drug caused a faster and greater decline in APD90 during the no-flow period. Resting tension did not change during 30 minutes of no-flow ischemia in the presence of pinacidil, and reperfusion led to 85% and complete recovery of electrical and mechanical activity at 1 and 10 microM, respectively. The data indicate that glibenclamide enhances whereas pinacidil reduces myocardial damage caused by ischemia/reperfusion. The results are consistent with the hypothesis that activation of ATP-regulated K+ channels during ischemia is an important adaptive mechanism for protecting the myocardium when blood flow to the tissue is compromised.

Transient inotropic effects of low extracellular sodium in perfused rat heart

The inotropic effects of low concentrations of extracellular Na+ (35-110 mM) were studied using Langendorff-perfused rat hearts. Low Na+ induced an initial positive inotropic response proportional to the decrease of transsarcolemmal Na+ gradient. At 35 mM Na+, this effect was followed by a secondary fall in contractility and rise of resting force (RF) and then by a delayed positive inotropic effect and recovery of RF. The magnitude of these low Na(+)-induced transient changes was dependent on the extracellular Ca2+ concentration and was altered by amiloride (6 x 10(-4) and 2.5 x 10(-3) M), ouabain (5 x 10(-5) and 5 x 10(-4) M), ryanodine (2 x 10(-8), 1 x 10(-7) and 1 x 10(-6) M), and sodium azide (1 x 10(-3) and 5 x 10(-3) M) but not by verapamil (2 x 10(-8) and 1 x 10(-7) M) or vanadate (4 x 10(-6) M). The data indicate the initial positive inotropic response of the rat heart to low Na+ may be due to rapid loading of myocytes with Ca2+ through the Na(+)-Ca2+ exchange mechanism. The secondary depression of contractility and the rise of RF appear to be the consequence of the short-lived intracellular Ca2+ overload. Furthermore, the recovery of contractions and the delayed positive inotropic response may be the result of the intracellular redistribution of excessive Ca2+ into the sarcoplasmic reticulum with mitochondria and increased transsarcolemmal Ca2+ efflux apparently playing a more minor role.

G proteins mediate suppression of Ca2+-activated K current by acetylcholine in smooth muscle cells

The role of G proteins in cholinergic suppression of Ca2+-activated K current was studied in isolated canine colonic myocytes with the whole cell voltage-clamp technique. Acetylcholine (ACh; 10.0 microM) caused a 64 +/- 2.4% depression in the Ca2+-dependent component of the outward current evoked at potentials between -45 and -15 mV when GTP (0.1 microM) was included in the pipette-filling solution. This effect was reversed within 2-4 min on washout of ACh. Without GTP in the filling solution, ACh caused a 15 +/- 2.5% depression in outward current in 60% of the cells tested. When the non-hydrolyzable GTP analogues, GTP gamma S (0.1 mM) or 5'-guanylylimidodiphosphate (GppNHp; 0.1 mM) were used, the decrease in outward current was greater (85 +/- 4.2 and 78 +/- 6.5%, respectively), and it was not reversed on withdrawal of ACh. Dialysis of the cell interior with pipette solution containing pertussis toxin (1 ng/ml) for 30 min had no effect on the whole cell currents evoked on depolarization, but it abolished the effect of ACh on Ca2+-dependent outward current. These data suggest that coupling of muscarinic receptors to the inhibition of Ca2+-activated K channels is mediated by pertussis toxin-sensitive G proteins in colonic smooth muscle cells. G protein-mediated inhibition is distinctly different from the opening of muscarinic-regulated K channels in other cell types.

Muscarinic suppression of Ca2+-dependent K current in colonic smooth muscle

Acetylcholine (ACh) increases the amplitude and duration of colonic electrical slow waves. This suggests that ACh either increases an inward current or suppresses an outward current. The latter hypothesis was tested in whole cell voltage-clamp experiments performed on freshly dispersed smooth muscle cells from canine proximal colon. Addition of ACh (10(-5) M) to solutions bathing cells reduced time-dependent outward currents elicited by depolarizing test pulses in the range of -45 to +30 mV. Analysis of tail currents showed that ACh caused a 10- to 15-mV positive shift in voltage-dependent activation. When cells were pretreated with 10(-6) M nifedipine to abolish the Ca2+-dependent component of the outward current, the reduction of outward current by ACh was blocked. Single-channel experiments were performed to determine whether ACh had a direct effect on Ca2+-activated K channels. ACh, 10(-5) M, added to bath and pipette solutions caused a positive shift in voltage-dependent activation in on-cell experiments. This effect of ACh on Ca2+-activated K channels provides a mechanism for the effects of muscarinic, excitatory stimulation of circular muscle of the colon.

Characterization of macroscopic outward currents of canine colonic myocytes

Outward currents of colonic smooth muscle cells were characterized by the whole cell voltage-clamp method. Four components of outward current were identified: a time-independent and three time-dependent components. The time-dependent current showed strong outward rectification positive to -25 mV and was blocked by tetraethylammonium. The time-dependent components were separated on the basis of their time courses, voltage dependence, and pharmacological sensitivities. They are as follows. 1) A Ca2+-activated K current sensitive to external Ca2+ and Ca2+ influx was blocked by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (0.1 X 10(-3) M) and nifedipine (1 X 10(-6) and was increased by elevated Ca2+ (8 X 10(-6) M) and BAY K 8644 (1 X 10(-6) M). 2) A "delayed rectifier" current was observed that decayed slowly with time and showed no voltage-dependent inactivation. 3) Spontaneous transient outward currents that were blocked by ryanodine (2 X 10(-6) M) were also recorded. The possible contributions of these currents to the electrical activity of colonic muscle cells in situ are discussed. Ca2+-activated K current may contribute a significant conductance to the repolarizing phase of electrical slow waves.

Gap junction uncoupling and discontinuous propagation in the heart. A comparison of experimental data with computer simulations

The effects of octanol on longitudinal propagation in guinea pig papillary muscles were measured by intracellular microelectrodes. These data were compared with alterations in conduction induced by stepwise removal of gap junction channels in computer simulations of propagation based on a discontinuous cable model. Octanol reduced the velocity (theta) of propagating action potentials (APs) from 53.2 +/- 3.5 to less than 6.6 +/- 2.1 cm/s before block occurred. The maximal rate of rise (Vmax) changed in a biphasic manner, increasing from 133.1 +/- 5.4 in controls to 201.7 +/- 11.0 V/s when theta was 20.5 +/- 2.8 cm/s, and then declining to less than 58.6 +/- 15.2 V/s just before block. The input resistance and time constant of the AP foot increased, and the ascending limb of phase-plane loops became increasingly nonlinear and notched during octanol treatment. All effects of octanol reversed upon washout. A strand of cardiac tissue was modeled as a discontinuous cable composed of 40 cells, each with 10 isopotential membrane segments described by Beeler-Reuter kinetics, and coupled by a variable number of gap junction channels (156 pS). Decreasing the number of channels from 40,000 to 400 to 60 slowed conduction from 62.6 to 16.4 to 3.1 cm/s. As noted in the experimental data, Vmax increased from 103 to 130 and then fell to less than 96 V/s. The AP foot increased and became nonexponential. Distinct notches developed during phase 1 of the APs at slower propagation velocities in the experiments and simulations. The close similarities between the experimental and theoretical data obtained in this study supports the applicability of a discontinuous cable model for describing longitudinal propagation in the heart.

Effects of calcium ionophore, A23187 and calmodulin inhibitors on intercellular communication in the rat myometrium

We have studied the effect of a calcium ionophore, A23187, and the purported calmodulin inhibitors, calmidazolium and chlorpromazine, on direct intercellular communication between smooth muscle cells in the myometrium of delivering rats. The extent of cell-to-cell coupling was determined by exposing one portion of small strips of longitudinal myometrium to 2-[3H] deoxy-D-glucose (2-DG) and determining the distribution and apparent diffusion coefficient (Da) for this tracer after a 5-h period for diffusion. The distribution and Da for 2-DG were significantly (p less than 0.05) reduced by exposure to A23187 in Krebs-Ringer solution with 2.5 mM Ca++, partially reduced in Krebs solution with A23187 and low Ca++ (1-10 microM), but the drug had no effect when used with Ca++-free solutions with [ethylenebis (oxyethylene-nitrilo)] tetraacetic acid (EGTA). The calmodulin inhibitors blocked the effects of A23187 in a dose-dependent fashion, and at higher concentrations, the extent of 2-DG diffusion was not different from that in control tissues. Surprisingly, however, a dose-dependent reduction in coupling was also observed in tissues exposed to the calmodulin inhibitors alone. Structural studies failed to reveal any change in the area of gap junctions between the myometrial cells following the above treatments, suggesting that the reduced exchange of 2-DG resulted from a decrease in the permeability of gap junctions between the muscle fibers.

Group psychotherapy as an aid in the medical treatment of eczema

The ongoing management of severe adult eczema is often difficult and problematic for both patient and doctor. A group of ten adult eczema patients were given group psychotherapy as a supplement to their regular medical regimen. Five target symptoms were rated on a biweekly basis first to establish individual baselines of disease course and later to measure treatment effect. The psychologic treatment combined behavioral and cognitive interventions with relaxation training. Patients used multiple self-rating sheets to provide feedback with the goal of increasing their skills in the management of scratching behaviors. At the end of treatment all ten patients showed significant reduction in targeted symptoms.

New 111In labeling of IgG: 111In-oxine mediated chelation

Current methods of 111In chelate conjugation labeling of antibodies expose the protein to pH 5-6 during 111In chelation. These conditions could be detrimental if the antibody is acid labile. We have successfully labeled human IgG via the cyclic anhydride of DPTA and 111In-oxyquinoline(oxine). Chelation was achieved at pH 6.9-8.4 and was complete within 1 min at room temperature. The chelation was sensitive to trace metal contamination on labware and in some reagents (including commercial 111In-oxine).

Comparative serum stability of radiochelates for antibody radiopharmaceuticals

Serum incubation of monoclonal antibodies chelate labeled by DTPA, benzyl-EDTA and benzyl-TETA with 111In, 57Co, and 67Cu demonstrated marked differences in their stability. In serum, 111In-benzyl-EDTA-antibody was more stable than 111In-DTPA-antibody. Cobalt-57 or 67Cu chelated antibody were less stable than either 111In chelated antibody; 67Cu was only firmly attached to the antibody as 67Cu-benzyl-TETA-antibody. The relative stability of the radiometal chelated antibodies was paralleled by the relative stability in serum of the radiometal chelates themselves. These in vitro studies suggest that in vivo behavior of metal chelates exposed to a complex protein environment cannot be predicted by classical equilibrium constants.

Evidence for physiological regulation of myometrial gap junction permeability

We have investigated whether direct intercellular communication between uterine smooth muscle cells of delivering rats is influenced by intracellular adenosine 3',5'-cyclic monophosphate concentration ([cAMPi]) and agents relevant to the hormonal control of pregnancy and parturition. The rate of diffusion of phosphorylated 2-[3H]deoxy-D-glucose (2-DG) in strips of longitudinal myometrium from rats in labor, indicated by the apparent diffusion coefficient for this molecule, was observed to be significantly reduced in tissues with elevated [cAMPi] (after treatment with dibutyryl cAMP, 8-bromo cAMP, forskolin, and theophylline) in the absence of any change in the area of gap junctions (GJs). Similarly, several agonists that elevate [cAMPi] in this tissue (e.g., isoproterenol, relaxin, carbacyclin, prostaglandin E2) also reduced 2-DG diffusion. These data suggest that the permeability of GJs in uterine smooth muscle may be regulated by [cAMPi] and physiologically relevant agonists. Control of GJ permeability may be important for the physiological regulation of intercellular communication and the extent of synchronous contractile activity in the uterine wall during pregnancy and parturition.

Serum stability of 67Cu chelates: comparison with 111In and 57Co

Simple chelates and chelate conjugated monoclonal antibodies labeled with 111In, 57Co and 67Cu demonstrate marked differences in stability when exposed to a serum environment. Among these radiometals, on DTPA, the order of stability is 111In greater than 57Co much greater than 67Cu. On benzyl-EDTA, the order of stability is 111In congruent to 57Co much greater than 67Cu. Among those investigated, the only serum stable 67Cu chelate found was 67Cu-TETA. The order of stability observed for 57Co vs 67Cu is contrary to published equilibrium constants. These in vitro studies suggest that the in vivo behavior of metal chelates exposed to a complex molecular environment may not be predicted by classically determined equilibrium constants.

Gap junctions and direct intercellular communication between rat uterine smooth muscle cells

We have tested the hypothesis that an increase in direct intercellular communication accompanies the development of gap junctions (GJs) between rat uterine smooth muscle cells at parturition. Intercellular communication in these tissues was studied by exposing one portion of small strips of myometrium to 2-[3H]deoxy-D-glucose (2-DG) and determining the longitudinal distribution of tracer after a 5-h period of diffusion. The distribution of 2-DG was greater in parturient compared with ante- and postpartum tissues. Similarly, the apparent diffusion coefficient of 2-DG was almost 10-fold greater in delivering tissues (1.86 X 10(-6) cm2/s) than before (0.199 X 10(-6) cm2/s) or after (0.296 X 10(-6) cm2/s) parturition. Control experiments indicated that the redistribution of 2-DG was dependent on the presence of GJs and was the result of intracellular and direct cell-to-cell diffusion. The appearance of GJs is the myometrium at term facilitates direct intercellular communication between uterine smooth muscle cells during labor. This improved communication may be responsible for synchronizing and coordinating electrical, metabolic, and contractile activity in the uterine wall and, hence, the effective expulsion of fetuses.

Copper chelates as probes of biological systems: stable copper complexes with a macrocyclic bifunctional chelating agent

Monoclonal antibodies tagged with chelated metal ions have numerous potential applications. Here we report the synthesis of a new "bifunctional" metal chelator, 6(p-bromoacetamidobenzyl)-1,4,8,11-tetraazacyclotetradecane- N,N',N",N"' -tetraacetic acid, which can be covalently attached to proteins and which binds copper stably in human serum under physiological conditions. In contrast, other reagents based on ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid rapidly lose copper to serum albumin under the same conditions.

Morphology of the pineal complex of the anadromous sea lamprey, Petromyzon marinus L

The pineal complex of the anadromous sea lamprey, Petromyzon marinus L., has been examined by light and electron microscopy. It consists of two subunits: a dorsomedial pineal organ, and a ventral, left-lateral parapineal organ, with both remaining cytologically unaltered throughout the life cycle. However, during metamorphosis there is an increase in the size and a rostral migration of the parapineal organ and a dorsolateral displacement of the pineal nerve tract. The pineal organ is composed of an end bulb, an atrium, and a nerve tract. Two varieties of photoreceptors, termed type I and type II cells, as well as supporting and ganglion cells are present. Supporting cells are ubiquitous, but there are regional variations in the distribution and abundance of the other cell types. Type I cells are a well-differentiated photoreceptor. Conversely, type II cells exhibit a poorly developed photosensory apparatus but possess some features commensurate with an endocrine activity. The parapineal organ is composed of an end bulb, a ganglion region, and a nerve tract. The end bulb is dominated by type II photoreceptor and supporting cells, whereas type I and ganglion cells are sparse. The parapineal ganglion and nerve tract include neuropil, polymorphic neurons, and ependymal cells. It is concluded that the pineal organ of P. marinus is a structurally well-developed photosensory and photoneuroendocrine organ that is probably capable of transducing photic stimuli into nervous and endocrine messages to the brain and other organs. In contrast, the parapineal of this lamprey species is a poorly developed organ of regressed or rudimentary structure.

The effect of pinealectomy, continuous light, and continuous darkness on metamorphosis of anadromous sea lampreys, Petromyzon marinus L

The role of the pineal complex in lamprey metamorphosis was investigated by examining the influence of pinealectomy and continuous light and darkness on the initiation of this event in anadromous sea lampreys, Petromyzon marinus L. Larval lampreys, which on the basis of a condition factor were considered likely to enter metamorphosis in July, were separated in May of 1979 and 1980 into the following groups: (1) intact controls, (2) sham-operated controls, (3) pinealectomized individuals, (4) those exposed to continuous light, and (5) those exposed to continuous light or dark. The importance of the pineal complex to metamorphosis was supported by morphological evidence that, in all presumably pinealectomized individuals that entered metamorphosis, the complex had apparently not been removed during the surgical procedure. The ways in which the pineal complex may be involved in lamprey metamorphosis are discussed.

Renal toxicity studies of protein-bound platinum(cis)

Incubation of dialyzed rat serum with cisplatin at a concentration of 908 ppm results in binding of platinum to the proteins and electrophoretic evidence of protein alterations. Intravenous administration of protein-bound platinum(cis), containing the same platinum content as an 8.5-mg/kg dose of cisplatin, fails to produce elevated serum BUN and creatinine levels as do equivalent doses of 'free' cisplatin in 0.9% saline. Light microscopy of the right side kidneys of rats receiving protein-bound platinum(cis) revealed no obvious pathology while the kidneys of rats receiving 'free' cisplatin showed consistent pathological alterations including hydropic degeneration and pyknotic nuclei. These observations suggest that a protein-bound form of platinum will be unlikely to contribute to the renal toxicity observed during cisplatin chemotherapy.

Preparation and metabolism of a cisplatin/serum protein complex

195mPt-cis-Dichlorodiammine platinum(II) (195mPt-cisplatin) binds in vitro essentially irreversibly to bovine serum albumin (BSA) and rat plasma proteins at a 195mPt-cisplatin/protein molar ratio of 1:1 or less. The binding to rat serum proteins shows no apparent specificity, with albumin retaining the greatest fraction of the label (40-55%). The binding is neither instantaneous nor linear with time. Upon intravenous administration to rats of a rat serum protein bound 195mPt-cisplatin, the label remains bound to the proteins while in the blood. The label is cleared from the blood faster than a relatively native 131I-labeled human serum albumin (HSA) and accumulates primarily in the liver. The blood disappearance and organ distribution of the rat serum protein bound 195mPt-cisplatin is consistent with a modified protein. Approx. 11% of the injected dose was excreted via the urine in 24 h in a form which has a different chromatographic mobility than free 195mPt-cisplatin. Since little intact protein is lost in the urine, the excreted label probably represents the product(s) of metabolism of the rat serum bound 195mPt-cisplatin. Due to the apparent irreversibility (both in vivo and in vitro) of the protein/195mPt-cisplatin complex, it is unlikely that the protein bound fraction of the administered 'free' drug will serve as a therapeutically useful 'drug resevoir'.

Filariasis in West Kalimantan (Borneo), Indonesia

A survey was carried out among persons residing in 8 villages in the Province of West Kalimantan, Indonesia to determine the prevalence of filariasis. Finger tip blood smears were obtained at night from over 3,000 people and microfilariae of Brugia malayi were found in 108 (3.5%) and Wuchereria bancrofti in 10 (0.3%). Most B. malayi (96 carriers) was found in Kakap, a village near the coast, 20 km from the provincial capital of Pontianak. Nine of 10 cases of W. bancrofti were located in Pahauman, a village 130 km northeast of the provincial capital. Periodicity studies indicate the strain of B. malayi to be subperiodic. In Kakap 18% of 226 persons examined had a clinical history of filariasis and elephantiasis was seen in 13%. This is the first report of rural bancroftian filariasis in the area. A few Mansonia species of mosquitoes were examined but none were infected with filarial larvae.

Parasitic infections in humans in West Kalimantan (Borneo), Indonesia

A survey was carried out among inhabitants of eight villages in West Kalimantan Province (Borneo), whereby blood smears were examined for malaria, stools examined for intestinal parasites and sera tested by the indirect hemagglutination test for antibodies to Entamoeba histolytica and toxoplasma gondii. The prevalence of malaria among 3017 people examined was 5.6% (Plasmodium vivax 2.8%, Plasmodium falciparum 2.8%). Brugia malayi microfilariae were found in 3.6% and Wuchereria bancrofti in 0.3%. Ninety-seven percent of 2101 stool specimens examined contained evidence of intestinal parasites. Trichuris trichiura (90%) was most common followed by Ascaris lumbricoides (76%), hookworm, (60%), Etamoeba coli (23%), Entamoeba histolytica (6%), Endolimax nana (6%), Iodamoeba butschlii (4%), Giardia lamblia (3%), Chilomastix mesnili (1%) and Strongyloides stercoralis (1%). Other parasites found were Entamoeba hartmanni, Trichomonas hominis, Balantidium coli, Enterobius vermicularis, Hymenolepis nana, Echinostoma sp. and Physalopterid, Dicrocoeliid, and Heterophyid type-eggs. The amoeba prevalence rate was 30%. Indirect hemagglutination antibody titers equal to or greater than 1:128 for Entamoeba histolytica and 1:256 for Toxoplasma gondii were detected in 7% and 3%, respectively, of 1511 sera tested.

Parasitology survey in northern Sumatra, Indonesia

A parasitology survey was conducted in five villages in North Sumatra, Indonesia. A total of 3,207 blood smears, 2,066 stool specimens and 969 sera were examined. Sixty (1.9%) inhabitants had malaria (Plasmodium vivax 41, P. falciparum 19), and 20 had Brugia malayi microfilaraemia. The most common intestinal helminths were Trichuris trichiura (87%), Ascaris lumbricoides (75%) and hookworm (58%). Other helminths found in low numbers were Enterobius vermicularis, Strongyloides stercoralis, Taenia sp., Fasciolid, Dicrocoeliid and Echinostoma sp. eggs. Entamoeba coli (25%) was the most common intestinal protozoa followed by Endolimax nana (8%), Entamoeba histolytica (7%), Giardia lamblia (6%), Iodamoeba bütschlii (5%), Entamoeba hartmanni (1%) and Chilomastix mesnili (1%). The amoeba prevalence rate was 31 per cent. Testing of sera for Entamoeba histolytica and Toxoplasma gondii antibodies by the indirect haemagglutination test demonstrated positive reactors in 13 per cent and nine per cent of the population respectively. The greatest number of seropositives for Toxoplasma gondii was at elevations of sea level to five meters and the lowest number at elevations of 5OO-1,000 meters.

Renal adenocarcinoma in an owl monkey (Aotus trivirgatus)

A renal adenocarcinoma in the right kidney of a 5-year-old female owl monkey is reported.