PATHWAYS THROUGH WHICH GLUCOSE INDUCES A RISE IN [CA2+]I OF POLYMORPHONUCLEAR LEUKOCYTES OF RATS

Basal levels of [Ca2+](i) are elevated in diabetes mellitus. Such an a bnormality is most likely due to both increased calcium influx into ce lls and decreased efflux of this ion out of the cells. The present stu dy examined the cellular pathways that are responsible for hvperglycem ia-induced acute rise in polymorphonuclear leukocytes (PMNL). and expl ored whether such a rise is due to increased calcium entry into PMNL a nd/or to calcium release from their intracellular stores. There were d ose dependent and time dependent rises in the [Ca2+](i) of PMNL expose d to high concentrations of glucose. Similar cffrcts were observed whe n the PMNL were exposed to high concentrations of choline chloride or mannitol. A substantial part of the rise in [Ca2+](i) was inhibited wh en the media contained verapamil or nifedipine or when the PMNL were p laced in calcium free media, and the rise in [Ca2+](i) was completely abolished when the PMNL were placed in calcium free media containing r yanodine. GDP beta S or pertussis toxin almost completely prevented th e glucose-induced rise in [Ca2+](i) of PMNL. Rp-cAMP, H-89 or staurosp orine produced significant inhibition of the rise in [Ca2+](i). High c oncentrations of glucose produced a dose dependent shrinkage of PMNL v olume over a period of two hours. The volume of PMNL. however, was nor mal after 24 hours in in vitro incubation studies as well as after 1.2 and 12 days of streptozotocin-induced hyperglycemia in rats. The resu lts are consistent with the formulation that the osmotic activity (cel l shrinkage) of the high glucose concentrations activates G protein(s) which then stimulates the adenylate-cAMP-protein kinase A pathway, ph ospholipase C system and calcium channels. The stimulation of these ce llular pathways permits both calcium influx into the PMNL as well as m obilization of calcium from their intracellular stores. Both of these events contribute to the acute rise in their [Ca2+](i). It is possible that the rise in [Ca2+](i) is critical for the stimulation of the eve nts that lead to the generation and accumulation of inorganic osmolyte s to restore cell volume to normal.