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R J Lang

Publications and source records attributed to R J Lang.

At least 37 records · Page 2Linked to original sources
PubMed1994

Identification of single transiently opening ("A-type") K channels in guinea-pig colonic myocytes.

Two K+ channel populations were identified in depolarized cell-attached membrane patches of myocytes freshly dispersed from the circular smooth muscle of guinea-pig proximal colon. First, a large-conductance (150 pS) Ca(2+)-activated K+ channel which was non-inactivating and sensitive to blockade by tetraethylammonium (TEA, 0.5-5 mM); and second, a smaller conductance K+ channel which opened and closed within 100 ms, was insensitive to TEA (0.5-5 mM), but was blocked by 5 mM 4-aminopyridine (4-AP) or maintained depolarization, and which had a unitary conductance of 12-13 pS. The averaged time course of these smaller conductance K+ channels closely resembled the time course of the 4-AP-sensitive, Ca(2+)-insensitive transient outward K+ current recorded in the whole-cell recording mode.

4-Aminopyridine↗
PubMed1994

Effects of intrinsic prostaglandins on the spontaneous contractile and electrical activity of the proximal renal pelvis of the guinea-pig.

1. The effects of blocking prostaglandin biosynthesis with indomethacin on the spontaneous electrical and contractile activity recorded in smooth muscle strips of the guinea-pig renal pelvis were examined using standard tension and membrane potential recording techniques. 2. Circumferentially cut strips of proximal renal pelvis contracted more frequently (4.5 +/- 0.2 min-1) than strips cut from the mid region (1.3 +/- 0.2; P < 0.05, n = 5) of the renal pelvis. 3. Indomethacin (1 nM-10 microM) reduced the amplitude and frequency of the contractions of the renal pelvis in a concentration- and time-dependent manner. Contractions were completely abolished in the presence of 30 microM indomethacin. 4. After indomethacin blockade, activation of prostaglandin F2 alpha (PGF2 alpha) receptors with dinoprost (1-100 nM) restored the amplitude and frequency of the spontaneous contractions of renal pelvis. Higher concentrations of dinoprost (> 100 nM-3 microM) increased the contraction amplitude of the proximal and mid renal pelvis 1.9 and 1.6 times respectively. The contraction frequency of the mid renal pelvis, but not the proximal pelvis, was also raised above its pre-indomethacin frequency. 5. The spontaneous electrical activity recorded in proximal strips of the renal pelvis was designated to come from three cell types: (i), pacemaker cells (10% of cells recorded), with simple action potentials comprising relatively slow rising and repolarizing phases triggered on top of a slowly-developing pre-potential; (ii), driven cells (75% of cells), with complex action potentials comprising a rapid initial spike, followed by a period of membrane oscillation and a plateau of 0.2-2 s duration; and (iii), intermediate cells (15%) which fired action potentials with an initial rapid and a long plateau phase. 6. Indomethacin (10-30 micro M) decreased the amplitude and frequency of the action potentials recorded in driven and intermediate cells. The membrane potential of these cells also depolarized 5mV to-51.2 +/-2.6mV (n=5).7. Dinoprost (300 nM-1.5 micro M) increased the rate of action potential discharge, without affecting the membrane potential of driven cells previously exposed to indomethacin (30 micro M).8. These data suggest that the endogenous release of prostaglandins is necessary for the in vitro spontaneous contractile activity recorded in the guinea-pig renal pelvis. Blockade of the synthesis of these prostaglandins appears either to modify the ability of the driven regions of the renal pelvis to fire action potentials or to reduce the coupling of these driven regions to their pacemaker cells.

Action Potentials↗
PubMed1993

Voltage-gated ionic currents in smooth muscle cells of guinea pig proximal colon.

Smooth muscle cells enzymatically dispersed from the circular muscle layer of the guinea pig colon were examined for the expression of voltage-gated ionic currents using the whole cell patch-clamp technique. Three outward currents and one inward current were identified and characterized. The inward current, at physiological potentials, was generated by a voltage-gated Ca2+ conductance that was permeable to Ba2+ but blocked by Cd2+ (0.1 mM) or nifedipine (10 microM). The three outward currents were carried by K+, abolished when cells were internally perfused with Cs+, and distinguished by their sensitivity to known K(+)-channel blockers. A K+ current dependent on Ca2+ entry was activated at potentials positive to -40 mV and abolished by low concentrations (2-5 mM) of tetraethylammonium (TEA). A delayed rectifier-type K+ current activated slowly at potentials positive to -30 mV, showed little inactivation, and was abolished by higher concentrations (> 5 mM) of TEA. A rapidly activating and inactivating transient outward K+ current (IKto), activated at potentials positive to -60 mV, was abolished by low concentrations (3-5 mM) of 4-aminopyridine and was relatively insensitive to TEA (10-126 mM) blockade. The overlapping steady-state activation and inactivation curves of IKto revealed a "window current" phenomenon between -60 and -40 mV. The rapid activation of IKto at membrane potentials more negative than those for Ca2+ current suggests that IKto will influence cell excitability by delaying the upstroke of the action potential. The present data provide an ionic basis for the regenerative excitatory activity in the circular muscle layer of the guinea pig proximal colon.

4-Aminopyridine↗
PubMed1991

Effects of okadaic acid and ATP gamma S on cell length and Ca(2+)-channel currents recorded in single smooth muscle cells of the guinea-pig taenia caeci.

1. The effects of inhibiting phosphatase activity on Ca(2+)-channel currents and cell shortening in single cells of the guinea-pig taenia caeci were investigated by whole-cell voltage clamp and video recording techniques. 2. Ca(2+)-channel currents were isolated by use of pipette solutions containing Cs, tetraethylammonium and adenosine triphosphate (ATP) (3 mM). Ca2+ or Ba2+ (7.5 mM) in the bathing solution acted as the charge carrier during inward current flow. 3. Ca(2+)-channel currents in 7.5 mM Ba2+ (IBa) were recorded at potentials positive to -40 mV, were maximal near 0 mV and reversed near +60 mV. Both the inward and outward flow of current was blocked by 100 microM Cd2+. 4. Addition of the ATP analogue, adenosine 5'-O(3-thiotriphosphate) (ATP gamma S) (1 mM) to the pipette solution (containing 3 mM ATP) caused cell shortening to 23 +/- 2% (n = 5) of their initial length within 5 min. Control cells (containing 4 mM ATP) did not contract during recording periods up to 60 min in duration. 5. IBa, recorded 1-2 min after membrane rupture, was 134 +/- 19 (n = 13) pA, compared with 209 +/- 25 (n = 5) pA in control cells, otherwise there were no significant time-dependent effects of ATP gamma S. In particular, ATP gamma S did not prevent the decrease in amplitude, nor the acceleration of inactivation when Ca2+ (7.5 mM) replaced Ba2+ as the permeating ion. 6. Okadaic acid (OA) (50 microM), a chemical inhibitor of phosphatase activity, produced similar effects when applied intracellularly. When OA (25,microM) was applied extracellularly the rate of rundown of 'Ba was slowed. 7. Isoprenaline (1 microM) alone had no effect on 'Ba, but induced a small increase in IBa in the presence of OA (25 microM). 8. Thus, our results indicate that (1) the contractions in ATP gamma S and OA may well arise from the activation of a kinase which phosphorylates myosin at low concentrations of Ca2 +, and (2) changes in the state of phosphorylation of Ca2+ channels, or associated proteins, in the taenia caeci modulate their function, but probably not via mechanisms involving cyclic AMP-dependent protein kinases.

Adenosine Triphosphate↗
PubMed1991

Effects of 2,3-butanedione monoxime on whole-cell Ca2+ channel currents in single cells of the guinea-pig taenia caeci.

1. The inhibitory actions of cadmium (Cd2+), nifedipine and 2,3-butanedione monoxime (BDM) on whole-cell Ca2+ channel currents in single cells of the guinea-pig taenia caeci were investigated using a single-electrode whole-cell voltage-clamp technique. 2. Calcium channel currents were isolated using pipette solutions containing Cs+, tetraethylammonium and ATP (3 mM). Ca2+ or Ba2+ (7.5 mM) in the bathing solution acted as the charge carrier during inward current flow. Ca2+ channel currents in 7.5 mM-Ba2+ (IBa) were recorded at potentials positive to -40 mV, were maximal near 0 mV and reversed near +60 mV. Ca2+ channel activation showed a sigmoidal relationship with potential, which was half-maximal at -13 mV. 3. Both the inward and outward flow of current was depressed and eventually blocked by 0.3-100 microM-Cd2+, 0.1-10 microM-nifedipine and 2-20 mM-BDM. Half-maximal blockade of IBa at 0 mV was achieved with approximately 3 microM-Cd2+, 1 microM-nifedipine and 10 microM-BDM. Steady-state activation curves were not affected by Cd2+ or BDM, but were shifted in the hyperpolarizing direction by nifedipine at concentrations > 1 microM. 4. Calcium channel currents in single cells and K+ contractures in intact strips were both blocked in a voltage-dependent manner. Steady-state inactivation curves (f infinity (V)) for IBa were shifted 20 mV in the hyperpolarizing direction by 0.3 microM-nifedipine and 4 mV by 10 mM-BDM. From these shifts a dissociation binding constant to inactivated Ca2+ channels for nifedipine was estimated as 78 nM, and for BDM, 5 mM. 5. At 10 microM Cd2+ produced a 43 +/- 6% (n = 3) block of the inward current at 0 mV when Ca2+ (7.5 mM) was the charge carrier (ICa), compared with the 36 +/- 3% block of IBa induced by 1 microM-Cd2+, consistent with the suggestion that Ca2+, Ba2+ and Cd2+ compete for the same binding site. In contrast, nifedipine (1 microM) and BDM (10 mM) blocked ICa more effectively than IBa. 6. Bay K 8644 (1.0 microM) increased Ca2+ channel currents two- to fourfold at all potentials due to a shift, of approximately 10 mV in the negative direction, of their activation curve and an equal shift in the positive direction of their inactivation curve. BDM (5-10 mM) could antagonize the action of Bay K 8644, shifting both curves back towards their control.(ABSTRACT TRUNCATED AT 400 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1990

The whole-cell Ca2+ channel current in single smooth muscle cells of the guinea-pig ureter.

1. Calcium channel currents were recorded in single, enzymatically isolated smooth muscle cells of the guinea-pig ureter using a single-electrode whole-cell voltage clamp technique. Calcium and barium currents through voltage-activated Ca2+ channels were recorded in cells dialysed with Cs(+)- or Na(+)-containing saline which suppressed K+ currents. 2. Inward currents in Ca2+ (1.5-7.5 mM) or Ba2+ (1.5-7.5 mM) were recorded at potentials positive to -50 to -30 mV. Inward currents were maximal at 0 mV in 1.5 mM-Ca2+ and at +10 mV in 7.5 mM-Ba2+. Current flow through Ca2+ channels in Cs(+)-filled cells (in 1.5 mM-Ca2+ or 7.5 mM-Ba2+) changed from inward to outward at potentials positive to +70 mV. In Na(+)-filled cells this reversal potential was between +50 and +60 mV. 3. Replacing Ca2+ or Ba2+ with Co2+ (1.5 mM) blocked all inward current flow through these Ca2+ channels; outward currents at potentials positive to +40 mV, however, were increased. Cadmium (100 microM) and nifedipine (0.1-10 microM) reduced both inward and outward current flow. 4. Calcium channel activation showed a sigmoidal relationship with membrane potential; the potential of half-maximal activation was -8.4 mV in 1.5 mM-Ca2+ and -10.8 mV in 7.5 mM-Ba2+. The maximum membrane conductance to Ca2+ (in 1.5 mM-Ca2+) was 2.57 nS/cell or approximately 0.05 mS/cm2. 5. Evidence for a voltage-dependent inactivation mechanism included (a) the time-dependent relaxation of the outward currents at potentials positive to the reversal potential and (b) a steady-state inactivation (f infinity (V] vs. membrane potential relationship (in 7.5 mM-Ba2+) which ranged between -80 and 0 mV, with a half-maximal availability at -40.5 mV. 6. The voltage dependencies of the inward current elicited from -80 and -30 mV were similar, suggesting that depolarization activated only L-type Ca2+ channels. 7. It was concluded that the processes controlling the time course of the Ca2+ current in single ureteral cells bathed in physiological concentrations of Ca2+ were mostly voltage-dependent.

Animals↗
PubMed1990

Stress-related symptoms among dental hygienists.

A sample of 49 practicing dental hygienists responded to a survey which included Derogatis and Spencer's 1982 Brief Symptom Inventory, a measure of stress-related symptoms, and a list of items considered stressful based on previous research with hygienists, arranged in six content categories. As hypothesized, in comparison with national norms, hygienists displayed significantly more symptoms on the over-all inventory and also on eight of nine subscales. Also as hypothesized, on the list of stressors, items pertaining to time pressure were rated as significantly more stressful than items from other behavioral domains. However, contrary to prediction, the correlation between over-all symptom level on the inventory and self-rated stress did not reach statistical significance. A variety of implications for stress reduction in dental hygiene practice are discussed.

Adult↗
PubMed1989

Identification of the major membrane currents in freshly dispersed single smooth muscle cells of guinea-pig ureter.

1. The passive and active electrical properties of freshly dispersed single cells of the guinea-pig ureter were investigated using standard patch-clamp techniques. 2. Action potentials, having a rapid rising phase and a prolonged plateau, were recorded on passing depolarizing currents through the patch pipette when 'near-normal' physiological gradients were established across the cell membrane (5.9 mM-K+, 1.5 mM-Ca2+ in the bath; 126 mM-K+ in the pipette). 3. Under voltage clamp, depolarization to potentials positive of -50 mV (from a holding potential of -70 or -80 mV) triggered a net inward current which reached a peak in 5-10 ms and then slowly inactivated. 4. The averaged membrane current to depolarization to potentials between -30 and 0 mV showed two distinct patterns after the peak of the inward current; the membrane current either moved slowly outward over 400 ms or there was one or more transient outward currents superimposed on the slowly decreasing inward current. Both outward currents were blocked when 5 mM-tetraethylammonium (TEA) was added to the bathing solution, resulting in an increased inward current at all potentials. 5. Replacing the extracellular Ca2+ with Co2+ (1.5-5 mM) blocked the inward current and the outward currents to reveal another transient outward current (voltage activated) which activated rapidly to reach a peak within 5 ms and which inactivated exponentially with a time constant of 10 ms. This voltage-activated outward current was inactivated if the membrane was held at -50 mV, but could be reactivated by short hyperpolarizing pre-pulses. The amplitude of this transient current in response to a fixed depolarization (to 0 mV) was half-maximum when the hyperpolarizing pre-pulse was to -66 mV. The voltage-activated outward current was reduced in amplitude when the extracellular potassium was raised to 46 mM or upon exposure to 1 mM-4-aminopyridine (4-AP), but was not affected by 5 mM-TEA. 6. Replacing K+ in the pipette and bathing solution with caesium (Cs) blocked all outward currents, revealing the time course and voltage dependence of the inward current, which could be carried by Ca2+ or Ba2+ with little effect on its rate of inactivation. 7. It was concluded that the inward current recorded in single ureter cells was due to the flow of current through voltage-activated Ca2+ channels. The TEA-sensitive outward currents, whether transient or slowly activating, are presumably K+ channels activated by Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Thy-1-mediated regulation of a low-threshold transient calcium current in cultured sensory neurons.

The physiological effect of ligand binding to the Thy-1 molecule expressed on the neuronal cell surface was examined. Sensory neurons obtained from dorsal root ganglia of 2-day-old CBA/CAH mice (Thy-1.2) were cultured in vitro for 8 days, and then patch-clamp recordings were obtained of calcium currents. It was found that binding of an anti-Thy-1.2 monoclonal antibody to neurons expressing the Thy-1.2 moiety increased the amplitude of a low-threshold transient calcium current. Monoclonal antibodies directed against the Thy-1.1 molecule or a neuronal surface ganglioside (A2B5) had no effect on this calcium current in Thy-1.2-bearing cells, nor did they interfere with subsequent activation by the anti-Thy-1.2 monoclonal antibody. These results demonstrate that ligand binding to the Thy-1 molecule transduces a physiological signal in sensory neurons by increasing a voltage-activated calcium current.

Animals↗
PubMed1988

Calcium currents in single isolated smooth muscle cells from the rabbit ear artery in normal-calcium and high-barium solutions.

1. Ca2+ inward current was studied using the whole-cell patch clamp technique in single smooth muscle cells enzymatically isolated from the rabbit ear artery. Currents were studied in salt solutions containing either normal (1.5 mM) Ca2+ or high (110 mM) Ba2+. Outward currents were minimized by using a high-Na+ intracellular solution containing 10 mM-TEA. 2. In normal-Ca2+ solution, the threshold at which inward current could be evoked was -60 mV at a holding potential of -80 mV and -48 mV at a holding potential of -60 mV. At both holding potentials, the current showed little inactivation over 500 ms near threshold, and inactivated substantially but incompletely with larger depolarizations. In high-Ba2+ solution where currents were 5-10 times larger, current threshold, maximal peak amplitude and apparent reversal potential were shifted in a positive direction along the voltage axis. 3. Inward current in normal-Ca2+ solution was only fully available negative to -90 mV, was half-inactivated near -47 mV and was about 90% inactivated at -10 mV. A component of non-inactivating current was, however, present in both normal-Ca2+ and high-Ba2+ solutions even after conditioning pulses of 5 s duration to +30 mV. The inactivation-potential relationship was shifted in a positive direction in high-Ba2+ solution, and its position showed considerable variation between cells. 4. The inward current from a holding potential of -70 mV was reduced in normal-Ca2+ solution by about 50% by nifedipine (0.1 microM) in some cells at all test potentials, although at more-negative test potentials peak current was unaffected in some cells even at 10 microM. In some cells when the holding potential was -90 mV, the peak current amplitude was increased markedly by 10 microM-nifedipine. In high-Ba2+ solution, from negative holding potentials (-70 to -80 mV), nifedipine augmented peak current at test potentials negative to -10 mV and shifted the current threshold in a negative direction; current at potentials positive of -10 mV was reduced. Both effects were concentration dependent. The stimulatory effect of nifedipine was abolished and its inhibitory effect was enhanced when less-negative holding potentials were employed. Bay K 8644 (0.1 or 1 microM) approximately doubled current amplitude in normal-Ca2+ solution at a holding potential of -60 or -70 mV, and shifted maximal peak and threshold current in a negative direction. 5. Holding at more-negative potentials made available a component of current which activated and inactivated at more-negative potentials especially in high-Ba2+ solution.(ABSTRACT TRUNCATED AT 400 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1987

Inward rectification in freshly isolated single smooth muscle cells of the rabbit jejunum.

1. Single smooth muscle cells were obtained by collagenase digestion of longitudinal muscle of rabbit jejunum. Membrane potential or current under voltage clamp was recorded by patch-clamp technique in the whole-cell recording mode at 22-25 degrees C. 2. At a membrane potential of -50 mV small hyperpolarizing current pulses produced electrotonic potentials which asymptotically approached a steady-state size and did not 'sag'. Stronger hyperpolarization resulted in a 'sag' of the electrotonic potential. Under voltage clamp an inward current, i, was activated in the range -60 to -110 mV. 3. This current had an equilibrium potential of -24.5 +/- 3.5 mV which was shifted negatively by reducing the sodium concentration, and positively by raising the potassium concentration of the bathing solution. 4. This current was blocked by caesium (1 mM) but less affected by barium ions up to 10 mM. 5. The time course of i upon stepping into its activation range was accelerated by increasing negativity and following an initial short delay could be described by a single exponential with a time constant in the range 60 s(-60 mV) to 1 s(-130 mV). 6. It is concluded that these jejunal cells possess a current to which sodium and potassium ions make a contribution which is responsible for the inward rectification they show upon hyperpolarization. This current is activated in a range which would allow it to contribute to the slow potential changes shown by longitudinal jejunal muscle.

Animals↗
PubMed1986

Electrophysiological analysis of projections of enteric inhibitory motoneurones in the guinea-pig small intestine.

The projections of neurones that produce inhibitory junction potentials (i.j.p.s) have been analysed in the small intestine of the guinea-pig. Intracellular microelectrodes were used to record i.j.p.s in circular muscle cells in response to stimulation with pairs of electrodes placed parallel to or across the length of the intestine (longitudinal and transverse electrodes, respectively). In preparations of circular muscle with the myenteric plexus attached, the mean amplitude of i.j.p.s recorded 9 mm lateral to longitudinal electrodes was about 70% of that seen at 1 mm; however, in the presence of hexamethonium (400 microM) the amplitude fell more rapidly to about 40% at 9 mm. The decline was even steeper in preparations of circular muscle from which the myenteric plexus had been removed, with the amplitude falling to 10% at 9 mm. I.j.p.s were detected up to 30 mm anal to stimuli applied with transverse electrodes in the presence of hexamethonium, but the decline was more rapid on the oral side, with i.j.p.s being detected only up to 12 mm oral to the stimulus. Nerves that travel through or originate in the myenteric plexus were severed or removed in operations performed 2-7 days before tissue was taken. 2-3 days after removal of a circumferential strip of myenteric plexus, i.j.p.s could not be recorded from the underlying circular muscle. I.j.p.s evoked by longitudinal electrodes were recorded in an area between two circumferential cuts through the myenteric plexus, 1.5-8 mm apart, 3-7 days after an operation. In this region, the i.j.p.s were significantly smaller than normal although amplitudes of up to 95% of control were measured. The consequences of single circumferential cuts through the myenteric plexus were examined 3 and 7 days after operation. Longitudinal electrodes were used to stimulate surviving fibres. Small i.j.p.s were recorded on the anal edge of the lesion; the amplitude recovered to 56% of normal in the first 2 mm on the anal side and the amplitude slowly returned to normal at 20 mm anal. On the oral side there was slight reduction in amplitude at 0.5 and 1 mm, but at greater distances amplitudes were normal. It is concluded that the simplest explanation of these results is that two populations of i.j.p.-producing neurones have their cell bodies in the myenteric plexus. Many axons supply the circular muscle close to or just anal to their cell bodies, and others run for various distances up to 30 mm in the anal direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1986

Calcium-activated potassium channels in single smooth muscle cells of rabbit jejunum and guinea-pig mesenteric artery.

Single-channel studies were made using the patch-clamp technique of K channels in dispersed single smooth muscle cells from rabbit longitudinal jejunal muscle and guinea-pig small (less than 0.2 mm o.d.) mesenteric arteries. In isolated inside-out patches from these two types of smooth muscle cell there was a population of K channels which had single-channel conductances of about 100 pS in near physiological K gradients and about 200 pS with symmetrical 126 mM-K solutions. Their conductance and other properties distinguish them from a K channel of smaller conductance which we have previously described in these cells. The relative permeability of the channel with respect to K was 1.4 Tl:1.0 K:0.7 Rb: less than 0.05 Na: less than 0.05 Cs. Cs (1 mM applied to the outside of the membrane) interfered with inward K movement when the membrane was hyperpolarized. Rb conductance of the channel when both sides of the membrane were exposed to 126 mM-Rb was 30 pS. When the Ca concentration on the inside of the membrane ([Ca]i) was about 10(-9) M, K channel opening was rarely observed and then only at strongly positive potentials. At [Ca]i between 10(-9) M and 10(-7) M mean channel open time increased and the probability of channel opening increased steeply; both were further increased by increasing membrane positivity. At [Ca]i between 10(-6) M and 2.5 mM the channel was mainly in the open state and the probability of channel conducting state often declined with increasing membrane positivity. The effects of varying [Ca]i from 10(-7) M to 2.5 mM on the kinetic activity of a single channel was studied largely in mesenteric artery patches containing one active channel. The distribution of open times could be fitted by a single exponential at low (less than 10(-6) M) [Ca]i but a component of fast openings (to less than 1.0 ms) was observed at all potentials at [Ca]i 2.5 mM. Closed time distribution required the sum of three exponentials to fit it all [Ca]i greater than 10(-7) M; at [Ca]i 10(-6) M or greater evidence of a fourth component, probably caused by Ca block of open channels, was obtained. Raising [Ca]i increased the mean duration of the (long) open state and decreased or had no effect on the duration of short, intermediate, and long mean closed states.

Action Potentials↗
PubMed1985

Patch and whole-cell voltage clamp of single mammalian visceral and vascular smooth muscle cells.

Dispersal of the constituent cells of mammalian visceral and vascular smooth muscles has permitted recordings both of membrane currents under whole-cell voltage clamp, and of currents through single ionic channels using the patch-clamp technique. A rectangular depolarizing step applied to a single cell under voltage clamp yielded a net inward current followed by a net outward current in normal physiological solution. In isolated, 'inside-out' patches of cell membrane a calcium- and potential-sensitive K channel (100 pS conductance) and a calcium-insensitive, potential-sensitive K+ channel (50 pS conductance) with slow kinetics have so far been identified and characterized.

Animals↗
PubMed1985

The mechanism of action of Ba2+ and TEA on single Ca2+-activated K+ -channels in arterial and intestinal smooth muscle cell membranes.

The interaction of Ba2+ and TEA with Ca2+-activated K+ channels was studied in isolated membrane patches of cells from longitudinal jejunal smooth muscle of rabbit and from guinea-pig small mesenteric artery (100 micron external diameter). Ba2+ applied from the inside of the membrane did not reduce unit current, except at high concentrations, but channels failed to open for long periods (s). This effect became much stronger when the potential gradient was in a direction driving Ba2+ into the channel and was reduced by increasing K+ ion concentration on the outside of the membrane. These results are consistent with Ba2+ entering the open channel and blocking at a site most of the way through the channel bore. In contrast, TEA and procaine dose-dependently reduced unit current amplitude at all patch potentials and slightly increased mean open time. Their effects were not detectably voltage-dependent and could be explained by TEA and procaine blocking the open channel with a timecourse that was faster than the frequency response of the recording system. The lack of appreciable voltage-dependence suggests that TEA and procaine bind to a site near to the inner mouth of the channel.

Animals↗