Evidence for contribution of Ca2+ storage sites on unitary K+ channel currents in inside-out membrane of rabbit portal vein.
While making use of the inside-out membrane patch, we examined the effects of caffeine and heparin on unitary currents of the large conductance Ca(2+)-dependent K+ (maxi-K+) channel in the rabbit portal vein. About half of the inside-out membranes we used contained a functional Ca(2+)-store site which facilitated modification of the maxi-K+ channel. When high-K+ solution containing 0.05mM EGTA was superfused in the bath, simultaneous openings of more than 20 maxi-K+ channels were observed in 39 of 83 patch membranes, and multi-channel opening appeared periodically or continuously at the holding potential of -10mV. Most channel activities of these patch membranes were inhibited by caffeine or heparin, and some heparin-insensitive channel activities were inhibited by caffeine. The remaining patch membranes (44 out of 83) showed low activity of the maxi-K+ channel, and neither caffeine nor heparin modified channel activity. Therefore, in our experimental set-up, half the number of excised patch membranes contained a Ca2+ store site. Most Ca2+ store sites have inositol 1,4,5-trisphosphate (InsP3)-activated Ca2+ release (IACR) and caffeine-activated Ca2+ release (CACR) channels and few lack the IACR channel. The mechanisms of activation of the maxi-K+ channel in relation to release of Ca2+ from the store sites can be examined in detail using the approaches we have described.
Xiong
Z L
ZL
Department of Pharmacology, Faculty of Medicine, Kyushu University, Japan.
Kitamura
K
K
Kuriyama
H
H
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D006493:Heparin / Q000494:pharmacology; D006652:Histological Techniques; D011169:Portal Vein / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology*; D011817:Rabbits
D015221:Potassium Channels; D002110:Caffeine; D004533:Egtazic Acid; D006493:Heparin; D002118:Calcium