Calcium-activated potassium channels in human platelets.
1. The effect of intracellular [Ca2+] ([Ca2+]i) on human platelet ion channels was studied using the nystatin whole-cell patch clamp recording technique. 2. Ionomycin-induced increases in [Ca2+]i rapidly activated a voltage-independent K(+)-selective channel with a slope conductance of 30 pS in 154 mM K+ saline. The single-channel conductance decreased in proportion to the square root of the external K+ concentration such that the estimated conductance in 5 mM K+ was approximately 5 pS. 3. The peak current under conditions expected to increase [Ca2+]i to micromolar levels indicated that each platelet possesses a small number (5-7) of 30 pS Ca(2+)-dependent K+ channels (KCa channels). 4. Spontaneous [Ca2+]i spiking was observed in many patch-clamped platelets using fura-2 fluorescence measurements. Each Ca2+ spike triggered up to five KCa channels at any one time. KCa channels were not active at resting levels of [Ca2+]i. 5. The results suggest that platelet KCa channels are not active under resting conditions but may have an important role in determining the membrane potential during Ca2+ signalling.
Mahaut-Smith
M P
MP
Physiological Laboratory, Cambridge, UK.
D001792:Blood Platelets / Q000187:drug effects* / Q000502:physiology; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005453:Fluorescence; D016257:Fura-2; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D013997:Time Factors
D015221:Potassium Channels; D015759:Ionomycin; D011188:Potassium; D002118:Calcium; D016257:Fura-2