Coexistence of two types of Ca(2+)-activated K+ channels in rat renal arterioles.
Single-channel K+ currents were characterized in vascular smooth muscle cells freshly isolated from preglomerular arterioles (15-40 microns OD) of the rat. Under conditions of symmetrical K+ (145 mM), two types of single-channel K+ currents with unitary slope conductances of 68 +/- 2.6 and 251 +/- 4.9 pS were recorded from excised inside-out membrane patches. The open state probability (NPo) of these two types of K+ channels was voltage sensitive and the channels were highly selective for K+ over Na+. Elevation of intracellular calcium concentration ([Ca2+]i) from 0.1 to 0.5 microM on the cytoplasmic face of inside-out patches increased the frequency of opening and the NPo of both the 68-pS and the 251-pS K+ channels. Application of ATP (0.1-1 mM) to the internal surface of inside-out patches had no effect on the activities of both channel types. Internally applied Ba2+ (1 mM) blocked both of these channels. Externally applied tetraethylammonium (0.1-0.3 mM) or charybdotoxin (50 nM) blocked both the 68-pS and the 251-pS K+ channels. Externally applied apamin (50 nM), however, selectively blocked the 68-pS K+ channel but had no effect on the frequency of opening of the 251-pS K+ channel. Apamin also reduced macroscopic K+ current recorded from voltage-clamped rat renal arteriolar muscle cells by 25-30%. These results indicate the coexistence of two types of Ca(2+)-activated K+ channels in the membranes of vascular smooth muscle cell isolated from renal preglomerular arterioles of the rat that differ in unitary conductances and pharmacological properties.
Gebremedhin
D
D
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226, USA.
Kaldunski
M
M
Jacobs
E R
ER
Harder
D R
DR
Roman
R J
RJ
D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001160:Arterioles / Q000166:cytology / Q000378:metabolism; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D018999:Charybdotoxin / Q000494:pharmacology; D004553:Electric Conductivity; D007477:Ions; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D012079:Renal Circulation; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D007477:Ions; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D018999:Charybdotoxin; D001030:Apamin; D001464:Barium; D019789:Tetraethylammonium; D002118:Calcium