DISTINCT SUBPOPULATIONS IN HACAT CELLS AS REVEALED BY THE CHARACTERISTICS OF INTRACELLULAR CALCIUM-RELEASE INDUCED BY PHOSPHOINOSITIDE-COUPLED AGONISTS

Intracellular calcium release induced by transient applications of pho sphoinositide agonists was measured using adherent single HaCaT kerati nocytes loaded with the acetoxymethyl derivative of fura-2, Applicatio n of ATP, bradykinin and formyl-Met-Leu-Phe (fMLP) resulted in a trans ient increase in intracellular calcium concentration ([Ca2+](i)) with an average half-width of 40 +/- 21 s and a decay time constant of 15 /- 10 s (mean +/- SD, n = 108), irrespective of the agonist applied. T he cells could be classified into two groups: in 53% of the cells repe ated stimulation brought about a progressively smaller change in [Ca2](i) (type 1 cells), whereas in the remaining cells the amplitude of t he calcium transients was essentially unchanged (type 2 cells). Furthe rmore, calcium transients in type 1 cells had broader half-widths and slower decays, No difference was found between the agonists in respect of the characteristics of the evoked calcium transient within each su bpopulation. However, bradykinin and fMLP desensitized some cells. The se results indicate that the activation of the inositol trisphospate t ransduction pathway by different agonists induces a characteristic ele vation of [Ca2+](i) within a given cell. Our results demonstrate that cultured HaCaT keratinocytes are heterogeneous in respect of the calci um transients evoked by the activators of this second messenger system .