Ca(2+)- and voltage-dependent gating of Ca(2+)- and ATP-sensitive cationic channels in brain capillary endothelium.
Biophysical properties of the Ca(2+)-activated nonselective cation channel expressed in brain capillaries were studied in inside-out patches from primary cultures of rat brain microvascular endothelial cells. At -40 mV membrane potential, open probability (P(o)) was activated by cytosolic [Ca(2+)] > 1 micro M and was half-maximal at approximately 20 micro M. Increasing [Ca(2+)] stimulated opening rate with little effect on closing rate. At constant [Ca(2+)], P(o) was voltage-dependent, and effective gating charge corresponded to 0.6 +/- 0.1 unitary charges. Depolarization accelerated opening and slowed closing, thereby increasing apparent affinity for Ca(2+). Within approximately 1 min of excision, P(o) declined to a lower steady state with decreased sensitivity toward activating Ca(2+) when studied at a fixed voltage, and toward activating voltage when studied at a fixed [Ca(2+)]. Deactivated channels opened approximately 5-fold slower and closed approximately 10-fold faster. The sulfhydryl-reducing agent dithiotreitol (1 mM) completely reversed acceleration of closing rate but failed to recover opening rate. Single-channel gating was complex; distributions of open and closed dwell times contained at least four and five exponential components, respectively. The longest component of the closed-time distribution was markedly sensitive to both [Ca(2+)] and voltage. We conclude that the biophysical properties of gating of this channel are remarkably similar to those of large-conductance Ca(2+)-activated K(+) channels.
Csanády
László
L
Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary. csanady@puskin.sote.hu
Adam-Vizi
Vera
V
D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001812:Blood-Brain Barrier / Q000502:physiology; D001921:Brain / Q000502:physiology*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002412:Cations; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000502:physiology*; D005439:Flufenamic Acid / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D051381:Rats
D015220:Calcium Channels; D002412:Cations; D005439:Flufenamic Acid; D000255:Adenosine Triphosphate; D002118:Calcium