Single calcium-dependent potassium channels in clonal anterior pituitary cells

290

144

SUMMARY1. 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 ( < 0-2 mm o.d.) mesenteric arteries.2. 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.3. The relative permeability of the channel with respect to K was 1-4 Tl: 1-0 K:0-7 Rb: < 0 05 Na: < 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. 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.

Section: Discussionsupporting

confidence: 58%

Section: Introductionmentioning

confidence: 96%

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

Benham¹,

Bolton²,

Lang³

et al. 1986

290

144

“…Open state probability (Popen) was measured as the fraction of time in which the current exceeded 50 % of the open amplitude (Barrett et al 1982). Occasional long quiescent periods (Barrett et al 1982;Wong et al 1982) (Magleby & Pallotta, 1983). Mean open and shut times were calculated as arithmetic means of duration of open and shut intervals.…”

Section: Methodsmentioning

confidence: 99%

“…Properties of Ca2+-activated K+ channels have been analysed on a single channel basis in a variety of cells, such as chromaffin cells (Marty, 1981;Yellen, 1984), skeletal muscle cells (Barrett, Magleby & Pallotta, 1982;Latorre, Vergara & Hidalgo, 1982;Magleby & Pallotta, 1983;Blatz & Magleby, 1984), smooth muscle cells (Benham, Bolton, Lang & Takewaki, 1986), acinar cells (Maruyama, Peterson, Flanagan & Pearson, 1983), pituitary cells (Wong, Lecar & Adler, 1982) and other cells (see Latorre, Oberhauser, Labarca & Alvarez, 1989). As to sensory hair cells, the properties of Ca2+-activated K+ channels have been studied in frog sacculus (Lewis & Hudspeth, 1983;Hudspeth & Lewis, 1988a, b;Roberts, Jacobs & Hudspeth, 1990), chick vestibular organ (Ohmori, 1984), mammalian and turtle cochlea (Ashmore & Meech, 1986;Art & Fettiplace, 1987;Kros & Crawford, 1990), chick and alligator cochlea (Fuchs, Nagai & Evans, 1988;, and goldfish sacculus (Sugihara & Furukawa, 1989).…”

Section: Sugiharamentioning

confidence: 99%

Calcium‐activated potassium channels in goldfish hair cells.

Sugihara

1994

1. Characteristics of Ca2"-activated K+ channels in the basolateral membrane of hair cells isolated from the caudal part of the goldfish saccular macula were studied mainly with the inside-out mode of the patch clamp method.2. Several types of Ca2"-activated K+ channels differing in unitary conductance were identified. The conductances (n = 156) ranged from 130 to 320 pS (when measured in symmetrical 125 mm KCl) and could be roughly separated into four groups, centred on values of 150, 200, 250 and 300 pS. The pharmacological profile, assessed by, for example, tetraethylammonium blockade, and the relatively large conductance indicated that these channels can be classified as large-conductance Ca2"-activated K+ channels (BK channels). The relative permeability of these channels to different ion species was in the order K+ (1P0) > Rb+(0 8) > NH4+ (04f14) > Na+, Cs+ (< 0 05). 10. The functional role of Ca2`-activated K+ channels in goldfish hair cells is discussed.

“…Blockade of voltage-dependent Ca2+-activated current by relatively low TEA concentrations has been shown in a number of cell types (Adams, Constanti, Brown & Clark, 1982c;Wong, Lecar & Adler, 1982;Yellen, 1984;Ritchie, 1987a;Marty & Neher, 1985), Similarly, apamin and curare have been shown to be relatively selective in blocking a voltage-independent, Ca2+-activated current in GH3 cells (Ritchie, 1987a, b;Lang & Ritchie, 1987), ganglionic neurones (Nohmi & Kuba, 1984;Dun, Jiang & Mo, 1986;Kawai & Watanabe, 1986;Goh & Pennefather, 1987), muscle (Romey & Lazdunski, 1984;Blatz & Magleby, 1986) and guinea-pig hepatocytes (Cook & Haylett, 1985). Using these agents, the following experiments test the possibility that rat chromaffin cell Ca2+-activated K+ current reflects the activation of two pharmacologically distinct currents.…”

Section: Ca2+-activated K+ Currents In Chromaffin Cellsmentioning

confidence: 99%

Two components of calcium‐activated potassium current in rat adrenal chromaffin cells.

Neely

Lingle

1992

104

129

1. The activation of calcium (Ca2+)‐dependent potassium (K+) currents in dissociated rat adrenal chromaffin cells was investigated using the dialysed cell recording technique. 2. Ca(2+)‐dependent K+ current was the major component of outward current at command potentials from ‐30 mV to about +50 mV. 3. Two components of Ca(2+)‐dependent outward current could be distinguished based on the voltage dependence of activation, the properties of tail currents following repolarization, and pharmacological properties. 4. One Ca(2+)‐dependent current was similar to an after‐hyperpolarization current (often termed IAHP) observed in other cell types. This current was largely blocked by 200 nM‐apamin or 200 microM‐curare, was associated with slow Ca(2+)‐dependent tail current, and exhibited little dependence on voltage. In cells with cytosolic Ca2+ buffered to 500 nM‐1 microM, curare‐sensitive current accounted for most of the membrane current at potentials negative to about ‐40 mV. 5. A second component of Ca(2+)‐activated K+ current exhibited voltage‐dependent activation, was completely blocked by 1 mM‐TEA, and turned off rapidly following repolarization. An unusual aspect of the TEA‐sensitive currents was that they appeared to inactivate under conditions of constant cytosolic Ca2+. 6. A novel observation during these experiments was a slow hump of outward current which appears to result from a non‐monotonic elevation in cytosolic Ca2+ during prolonged voltage jumps.