CUTANEOUS TRANSPORT OF CA2-PIPIENS - SIGNIFICANCE AND SPECIFICITY( INTHE FROG RANA)

Rana pipiens were divided into four groups: controls; hypocalcemic fro gs, depleted of salts by acclimation to deionized water; hypercalcemic frogs, calcium-loaded by the introduction of 40 mu mol calcium glucon ate; and frogs exposed to the potential competing ions Mg2+, Sr2+, and Ba2+. All groups displayed calcium influx that was proportional to ex ternal [Ca2+]; however, the group acclimated to deionized water also d isplayed hypocalcemia (P < 0.025) and enhanced Ca2+ influx at higher ( >0.3 mM) external [Ca2+]. Ca2+ efflux was depressed in hypocalcemic fr ogs, and thus net Ca flux shifted from net loss in control frogs to ne t uptake in hypocalcemic frogs. Hy pocalcemia also resulted in increas ed skin Ca2+ deposits which may be related to a decreased Ca2+ (and ot her ions) permeability as a consequence of the acclimation to deionize d water. Another group of frogs was Ca2+-loaded by injecting calcium g luconate. Sodium gluconate controls did not significantly alter Ca2+ f luxes. The frogs that received calcium gluconate treatments became hyp ercalcemic (P < 0.01) and did not display significant changes in calci um fluxes, nor did they show significant changes in skin calcium depos its. We conclude that hypocalcemia leads to regulatory responses that stimulate active Ca2+ transport in Rana pipiens skin and possibly inhi bits cutaneous and renal efflux. We also conclude that hypercalcemia d oes not alter calcium fluxes across skin. The ions from Group IIA of t he Periodic Table of Elements had little effect on Ca2+ fluxes at conc entrations ranging from 0.5-4.0 mM; neither Sr2+ or Ba2+ affected Ca2 influx. The only divalent ion tested that influenced Ca2+ was Mg2+ wh ich significantly inhibited Ca2+ influx but only at 4.0 mM or eight ti mes the external [Ca2+]. We conclude, therefore, that the Ca2+ transpo rt mechanism is fairly specific for Ca2+ within Group IIA. (C) 1997 Wi ley-Liss, Inc.