Intracellular Ca2+ transients in HT29 cells induced by hypotonic cell swelling

Cell swelling induced by hypotonic solution led to an osmolality-dependent increase in intracellular Ca2+ activity ([Ca2+]i) in HT29 cells. At moderate reductions in osmolality from 290 to 240 or 225 mosmol/l in most cases only a small monophasic increase of [Ca2+]i to a stable plateau of 10-20 nmol/l above resting [Ca2+]i was observed. Lower osmolalities resulted in a triphasic increase of [Ca2+]i to a peak value. In a first phase after the volume change, lasting 20-40 s, [Ca2+]i increased slowly by about 30 nmol/l. Thereafter [Ca2+]i increased more rapidly within 20-30 s to a peak value. This peak was 189 +/- 45 nmol/l (190 mosmol/l, n = 9) and 243 +/- 41 nmol/l (160 mosmol/l, n = 20) above resting [Ca2+]i. The peak was then followed by a decline of [Ca2+]i over the next 2-3 min to a stable plateau value of 28 +/- 6 (n = 6) and 32 +/- 11 nmol/l (n = 11) above resting [Ca2+]i at 190 and 160 mosmol/l, respectively. The plateau lasted as long as the hypotonic solution was present. Under Ca(2+)-free bath conditions the peak value for the cell-swelling-induced [Ca2+]i transient was reached significantly later (60-100 s, compared to 40-60 s under control conditions). The peak values under Ca(2+)-free conditions were not significantly lower. This indicates that the [Ca2+]i peak was mostly of intracellular origin. No [Ca2+]i plateau phase was observed under Ca(2+)-free bath conditions.(ABSTRACT TRUNCATED AT 250 WORDS)