Characterization of a newly found stretch-activated KCa,ATP channel in cultured chick ventricular myocytes.
With the use of the patch-clamp technique, five kinds of stretch-activated (SA) ion channels were identified on the basis of their single-channel conductances and ion selectivities in cultured chick ventricular myocytes. Because a high-conductance K+-selective channel predominated among these channels, we concentrated on characterizing its properties mostly using excised inside-out patches. With 145 mM KCl solution in the pipette and the bath, the channel had a conductance of 199.8 +/- 8.2 pS (n = 22). The ion selectivities among K+, Na+, Ca2+, and Cl- as estimated from their permeability ratios were PNa/PK = 0.03, PCa/PK = 0.025, and PCl/PK = 0.026. The probability of the channel being open (Po) increased with the Ca2+ concentration in the bath ([Ca2+]b; dissociation constant Kd = 0.51 microM at +30 mV) and membrane potential (voltage at half-maximal Po = 39.4 mV at 0.35 microM [Ca2+]b). The channel was blocked by gadolinium, tetraethylammonium, and charybdotoxin from the extracellular surface and, consequently, was identified as a Ca2+-activated K+ (KCa) channel type. The channel was also reversibly activated by ATP applied to the intracellular surface (Kd = 0.74 mM at 0.10 microM [Ca2+]b at +30 mV). From these data taken together, we concluded that the channel is a new type of KCa channel that could be designated as an "SA KCa,ATP channel." To our knowledge, this is the first report of KCa channel in heart cells.
Kawakubo
T
T
Department of Internal Medicine III, Nagoya University School of Medicine, Nagoya 466-8550, Japan.
Naruse
K
K
Matsubara
T
T
Hotta
N
N
Sokabe
M
M
D000227:Adenine Nucleotides / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D002642:Chick Embryo; D004553:Electric Conductivity; D004594:Electrophysiology; D006352:Heart Ventricles; D007477:Ions; D007700:Kinetics; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010812:Physical Stimulation; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism* / Q000502:physiology; D011312:Pressure
D000227:Adenine Nucleotides; D007477:Ions; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D000255:Adenosine Triphosphate; D002118:Calcium