CALMODULIN CONTENT IN PANCREATIC-ISLETS AND THE RESPONSE OF ISLET MEMBRANE CA2-DEPLETION( ATPASE TO CALMODULIN IN PHOSPHATE)

Chronic phosphate depletion is associated with a reduced V-max of Ca2 ATPase in many cells. The mechanisms underlying this phenomenon are n ot fully understood. One of the regulators of the Ca2+ ATPase enzyme i s calmodulin, and the reduced availability of calmodulin or impaired i nteraction between it and Ca2+ ATPase could be responsible for the imp aired activity of this enzyme in phosphate depletion. The present stud y examined the calmodulin content of pancreatic islets and the effect of calmodulin on the V-max of Ca2+ ATPase in islets harvested from pho sphate-depleted (PD) and pair-weighed (PW) rats. The calmodulin conten ts in islets from the 2 groups of animals were not different. Basal le vels of V-max of Ca2+ ATPase of islets from PD rats were significantly (p<0.01) lower than in PW rats. Calmodulin produced a significant (p< 0.01) increase in V-max of Ca2+ ATPase in islets of PW rats but failed to do so in islets of PD rats. The results indicate that the impaired activity of Ca2+ ATPase in islets of PD rats is not due to the reduce d availability of calmodulin but an impaired response of the enzyme to calmodulin is at least partly responsible for the reduction in the V- max of the enzyme.