Reciprocal regulation of K+ channels by Ca2+ in intact human T lymphocytes

The requirement for increased [Ca2+]i during T cell activation is well established. In the present study, we have used the cell-attached configuration of the patch-clamp technique and Ca2+ spectrofluorometry to investigate the regulation of K+ channel activity by intracellular calcium [Ca2+]i in intact human T lymphocytes. The predominant ion current in resting human T cells is a voltage-dependent K+ current, K(V), which is susceptible to second-messenger regulation. We report here that K(V) channel activity is reversibly inhibited at all relevant membrane potentials by a rise in [Ca2+]i induced by Ca2+ ionophore or the mitogens, concanavalin A or phytohemagglutinin. Consistent with this Ca2+ dependence, lowering [Ca2+]i with Ca(2+)-depleted medium can induce K(V) channel activity in otherwise quiet patches. We have also found two Ca(2+)-activated K+ channels (K(Ca)), a 9 pS channel and an inwardly rectifying 11-25 pS channel, similar to those we found in rat thymic T cells and human B cells. The sensitivity of these K(Ca) channels to [Ca2+]i suggests reciprocal regulation with that of K(V) channels. A considerable lag between mitogen treatment and induction of 9 pS K(Ca) activity, the decrease in this channel's activity in the continued presence of high [Ca2+]i or upon patch excision, and the decreased sensitivity of K(V) to Ca2+i block in disrupted cells all argue for the involvement of intracellular factors. During [Ca2+]i-mediated inhibition of K(V) channels, the recruitment of distinct K(Ca) channels is likely to play a central role in maintaining cell hyperpolarization and a sustained driving force for Ca2+ influx during T-cell activation.