FIBROBLAST AND EPIDERMAL GROWTH-FACTOR RECEPTOR EXPRESSION IN XENOPUSOOCYTES DISPLAYS DISTINCT CALCIUM OSCILLATORY PATTERNS

Electrophysiological study performed with the voltage clamp technique was used to examine the intracellular calcium pathway activated by tyr osine kinase receptor members. Three FGF receptors from Pleurodeles PR 1, PR3, PR4, homologs to human receptors, and the human EGF receptor w ere expressed in Xenopus oocytes. Under FGF1, FGF2 and FGF4 stimulatio n, PR1 and PR3 display a one phase inward chloride calcium dependent c urrent superimposed by sustained oscillations, whereas PR4 did not sho w any oscillations. These currents were dependent on intracellular cal cium mobilisation, as the responses were reduced by caffeine (10 mM. S olely PR4 responses were affected by an extracellular calcium depleted solution suggesting the involvement of concomitant extracellular and intracellular calcium intervention in the calcium chloride current, wh ereas PR1 and PR3 did not. Under EGF stimulation, the EGF receptor eli cits a two component inward current composed of an undelayed rapid tra nsient dependent on intracellular calcium store recruitment followed b y a second slower current dependent on calcium influx. The specific pa ttern and amplitude of the calcium oscillations induced by the combina torial action of growth factors on their receptors could be relevant i n numerous calcium dependent cell functions. 0167-4889/98/$ - see fron t matter (C) 1998 Published by Elsevier Science B.V, All rights reserv ed.