Heterogeneity of lymphocyte calcium metabolism is caused by T cell- specific calcium-sensitive potassium channel and sensitivity of the calcium ATPase pump to membrane potential
Calcium management differs in T and B lymphocytes. [Ca2+]i elevation in response to calcium ionophores is up to 10 times greater in T cells than B cells. There is no difference between them in ionophore uptake. T cells, but not B cells, possess a calcium-sensitive potassium channel which produces membrane hyperpolarization at [Ca2+]i above 200 nM. This alters T cell density providing a rapid and easy method of cell separation. In contrast, B cells depolarize when [Ca2+]i is increased. Isolated B cell membrane vesicle ATP-dependent calcium pump activity is higher than T cell vesicles. Membrane depolarization reduces the [Ca2+]i response to ionomycin, most dramatically in T cells because they are hyperpolarized by increased [Ca2+]i. The most likely basis of this behavior is an effect of membrane potential on lymphocyte membrane calcium pump activity. This mechanism provides an explanation of the inhibitory effect of membrane depolarization on T lymphocyte responses.