Inhibition of Na+/Ca2+ exchange in renal BLMV by IP3 depends on site of action and direction of Ca2+ flux.
It has previously been shown in synaptosomes that inositol 1,4,5-trisphosphate (1,4,5-IP3) inhibits Ca2+ transport by the plasma membrane-bound Na+/Ca2+ exchanger. The present study was therefore designed to determine if the effect of 1,4,5-IP3 was dependent on its site of action at the plasma membrane or on the direction of Ca2+ flux. To investigate this possibility, studies were performed in basolateral membrane vesicles (BLMV) isolated from rat renal cortex. As with synaptosomes, Ca2+ transport was inhibited by 1,4,5-IP3 in a concentration-dependent manner. At a concentration of 10(-6) M, 1,4,5-IP3 significantly (P < 0.005) inhibited Ca2+ transport by 36%. When Ca2+ transport was carried out in inside-out vesicles, 10(-6) M 1,4,5-IP3 significantly (P < 0.002) increased the degree of inhibition by an additional 75% (63 vs. 36%). However, 1,4,5-IP3 had no significant effect on Ca2+ transport in inside-out vesicles when Ca2+ flux was reversed (i.e., Ca2+ efflux). These data in renal BLMV confirm the novel action of 1,4,5-IP3 on the Na+/Ca2+ exchanger previously described in brain synaptosomes. These results also suggest that the action of 1,4,5-IP3 depends on both its site of action at the plasma membrane and on the direction of Ca2+ flux.
Fraser
C L
CL
Department of Medicine, Veterans Affairs Medical Center, San Francisco, California 94121.
Cummings
C
C
Cassafer
G
G
D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007668:Kidney / Q000378:metabolism*; D007672:Kidney Cortex / Q000378:metabolism; D007700:Kinetics; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014634:Valinomycin / Q000494:pharmacology
D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D014634:Valinomycin; D015544:Inositol 1,4,5-Trisphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium