Effect of Ca2+ agonists in the perfused liver: determination via laser scanning confocal microscopy

1 Department of Surgery; 2 Division of Metabolism, Department of Internal Medicine; and 3 Research Unit, Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110 Ca 2+ is a critical intracellular second messenger, but few studies have examined Ca 2+ signaling in whole organs. The amplitude and frequency of Ca 2+ oscillations encode important cellular information. Using laser scanning confocal microscopy in the indo 1 acetoxymethyl ester dye-loaded rat liver, we investigated the effect of various Ca 2+ agonists that act at distinct mechanistic sites on Ca 2+ signaling. Perfusion with suprathreshold doses of arginine vasopressin (AVP) (2-20 nM) caused a single Ca 2+ wave that originated in the pericentral vein region and spread centrifugally to the periportal area. Lower doses of AVP (0.2-2 nM) caused multiple Ca 2+ waves and Ca 2+ oscillations. Perfusion with ATP (1.4-17.5 µM) caused rapid transient elevations in intracellular free Ca 2+ concentration ([Ca 2+ ] i ) occurring in isolated hepatocytes or groups of hepatocytes throughout the lobule and were of shorter duration than those due to AVP. Also in contrast to AVP, there was no specific anatomic location within the hepatic lobule that was more susceptible to ATP. Thapsigargin and cyclopiazonic acid did not cause a Ca 2+ wave but rather produced a uniform and fairly simultaneous increase in [Ca 2+ ] i in all hepatocytes in the lobule. Perfusion with 14 µM ryanodine produced a single transient spike in [Ca 2+ ] i in a small number (