Novel effects of propranolol: Release of internal Ca 2+ followed by activation of capacitative Ca 2+ entry in Madin Darby canine kidney cells

Abstract

The effect of propranolol on Ca 2+ signalling in Madin Darby canine kidney (MDCK) cells was investigated by using fura-2 as a Ca 2+ probe. Propranolol increased cytosolic free Ca 2+ levels ([Ca 2+] i) in a concentration-dependent manner between 0.1 and 1 mM. The response was partly inhibited by external Ca 2+ removal. In Ca 2+-free medium pretreatment with 0.2 mM propranolol partly inhibited the [Ca 2+] i rise induced by 1 μM thapsigargin, an inhibitor of the endoplasmic reticulum Ca 2+ pump; but pretreatment with thapsigargin abolished propranolol-induced Ca 2+ release. Addition of 3 mM Ca 2+ induced a [Ca 2+] i rise after pretreatment with 0.2 mM propranolol in Ca 2+-free medium. Propranolol (0.2 mM) inhibited 25% of thapsigargin-induced capacitative Ca 2+ entry. Suppression of 1,4,5-trisphosphate (IP 3) formation by 2 μM U73122, a phospholipase C inhibitor, did not alter 0.2 mM propranolol-induced internal Ca 2+ release. Propranolol (1 mM) also increased [Ca 2+] i in human neutrophils. Collectively, we have found that 0.2 mM propranolol increased [Ca 2+] i in MDCK cells by releasing Ca 2+ from thapsigargin-sensitive Ca 2+ stores in an IP 3-independent manner, followed by Ca 2+ influx from external space. Independently, propranolol was able to inhibit thapsigargin-induced capacitative Ca 2+ entry.