Effects of modulators of cytosolic Ca2+ on phytohemagglutin-dependent Ca2+ response and interleukin-2 production in Jurkat cells.

Abstract

We have previously reported the presence, in Jurkat T cells, of outward K+ currents and inward currents that have been attributed to Ca2+ channels. Here, we have studied the effects of dimethyl 1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridine-dicarboxylate (nifedipine) and 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5- methoxy-carbonylpyridine-3-carboxylate (PN200-110), two dihydropyridines (DHPs) known to inhibit voltage-dependent Ca2+ channel activity in different types of cells, and two inhibitors of internal Ca2+ release (muscle cells), ryanodine and 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8), on the Phaseolus vulgaris phytohemagglutinin (PHA)-dependent responses in Jurkat T lymphocytes. Our results show that nifedipine and PN200-110 inhibit the PHA-dependent production of interleukin-2 except when 12-O-tetradecanoyl-13-O-acetyl phorbol is added to the cultures. Ryanodine and TMB-8 are not inhibitors. The PHA-dependent Ca2+ response is significantly reduced when the cells are preincubated in the presence of the DHPs. Under these conditions, ryanodine has only a small inhibitory effect and TMB-8 has no effect. In contrast, only ryanodine (50 microM) decreases the PHA-dependent cytosolic release of Ca2+i when the cells are bathed in a medium containing a low concentration of Ca2+ (60 nM). The inhibitory effects of nifedipine and PN200-110 may result from the binding of these DHPs to specific receptor sites as revealed by studies using [3H]PN200-110 (KD = 8.5 +/- 3.1 nM; 2300 +/- 500 apparent binding sites/cell). Photoaffinity labeling studies using [3H]azidopine as a probe showed specific incorporation of label into three glycoproteins of molecular mass (+/- SD) 170 +/- 13, 110 +/- 25, and 60 +/- 17 kd as analyzed by electrophoresis under reducing conditions.