Ca(2+)-activated K+ channels in rat thymic lymphocytes: activation by concanavalin A.
1. The role of ion channels in the mitogenic response of rat thymic lymphocytes to concanavalin A (ConA) was studied using single-channel patch-clamp recordings and measurements of membrane potential with the fluorescent probe bis-oxonol. 2. ConA (20 micrograms ml-1) evoked a rapid membrane hyperpolarization; Indo-1 measurements indicated a concurrent increase in [Ca2+]i. The hyperpolarization was blocked by cytoplasmic loading with the Ca2+ buffer BAPTA (bis(O-amino-phenoxy)ethane-N,N,N',N'-tetraacetic acid), or charybdotoxin, a component of scorpion venom known to block K+ channels in lymphocytes. 3. Cell-attached patch-clamp recordings showed that both ConA and the Ca2+ ionophore ionomycin activated channels with high selectivity for K+. Two conductance levels were observed -6-7 pS and 17-18 pS-measured as inward chord conductance at 60 mV from reversal potential (Erev) with 140 mM-KCl in the pipette. The current-voltage relationship for the larger channel displayed inward rectification and channel open probability was weakly dependent upon membrane potential. 4. These experiments provide the first direct evidence for mitogen-activated Ca(2+)-gated K+ channels (IK(Ca)) in lymphocytes. This conductance is relatively inactive in unstimulated rat thymocytes but following the intracellular Ca2+ rises induced by ConA, IK(Ca) channels are activated and produce a significant hyperpolarization of the cell potential.
Mahaut-Smith
M P
MP
Physiological Laboratory, Cambridge.
Mason
M J
MJ
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D018999:Charybdotoxin; D003208:Concanavalin A / Q000494:pharmacology*; D005456:Fluorescent Dyes / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012604:Scorpion Venoms / Q000494:pharmacology; D013268:Stimulation, Chemical; D013601:T-Lymphocytes / Q000502:physiology*; D013858:Thiobarbiturates / Q000494:pharmacology
D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D007211:Indoles; D015221:Potassium Channels; D012604:Scorpion Venoms; D013858:Thiobarbiturates; D003208:Concanavalin A; C059587:Indo-1 pentaacetoxymethyl ester; D018999:Charybdotoxin; C025284:bis(1,3-diethylthiobarbiturate)trimethineoxonol; D015759:Ionomycin; D002118:Calcium