A newly identified Ca2+ dependent K+ channel in the smooth muscle membrane of single cells dispersed from the rabbit portal vein.
We found a new type of Ca2+-dependent K+ channel in smooth muscle cell membranes of single cells of the rabbit portal vein. A slope conductance of the current was 180 pS when 142 mM K+ solution was exposed to both sides of the membrane (this channel was named the KM channel, in comparison to the known KL and KS channels from the same membrane patch; Inoue et al. 1985). This KM channel was less sensitive to the cytoplasmic Ca2+ concentration, [Ca2+]i, but was sensitive to the extracellular Ca2+, [Ca2+]o, e. g. in the outside-out membrane patch, lowering the [Ca2+]o in the bath markedly reduced the open probability of this channel, and also in cell-attached configuration, lowering of the [Ca2+]o using the internally perfused patch clamp electrode device reduced the opening of KM channel. TEA+ (1-10 mM) reduced the amplitude of the elementary current through the KM channel applied from each side of the membrane, but this agent inhibited the KM channel to a greater extent when applied to the inner than to the outer surface of the membrane. Furthermore, this KM channel had a weak voltage dependency, and the open probability of the channel remained much the same within a wide range of potential (from -60 mV to +60 mV). Whereas most Ca2+-dependent K+ channels are regulated mainly by [Ca2+]i and possess a voltage dependency, these properties of the KM channel differed from other Ca2+-dependent K+ channels.(ABSTRACT TRUNCATED AT 250 WORDS)
R
R
Inoue
K
K
Okabe
K
K
Kitamura
H
H
Kuriyama
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D011169:Portal Vein / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D007473:Ion Channels; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D011188:Potassium; D002118:Calcium