Caerulein and carbamoylcholine stimulate pancreatic amylase release at resting cytosolic free Ca2+

Abstract

Cytosolic free calcium concentrations ([Ca2+](i)) and amylase secretion were measured in isolated rat pancreatic acini loaded with the intracellularly trapped fluorescent indicator quin2. Both caerulein and carbamoylcholine caused a rapid increase in [Ca2+](i), with a maximal 3-fold increase at 10-9 M-caerulein and 10-4 M-carbamoylcholine. However, caerulein (10-12 M and 10-11 M) as well as carbamoylcholine (10-7 M) caused a significant stimulation of amylase release, while not inducing any detectable rise in [Ca2+](i). Changes in [Ca2+](i) after addition of either secretagogue were transient and did not last more than 2-3 min. By contrast, when amylase secretion was monitored as a function of time, two distinct secretory phases could be observed upon addition of either carbamoylcholine (10-5 M) or caerulein (10-10 M). An initial, rapid phase (0-5 min) which caused a 6-7-fold increase above basal, followed by a sustained (5-30 min), but less marked, secretory rate (2-3-fold above basal). Addition of atropine (10-4 M) 5 min after carbamoylcholine (10-5 M) (i.e. after termination of the rise in [Ca2+](i) and of the first secretory phase) did not cause any significant change in [Ca2+](i), while significantly inhibiting amylase secretion from 5 to 30 min to the same rate observed in the absence of the secretagogue. These results show that caerulein and carbamoylcholine, two agents thought to activate secretion mainly through mobilization of Ca2+ from intracellular stores, are capable of eliciting amylase secretion independently of a concomitant rise in [Ca2+](i). Furthermore, with both secretagogues the rise in [Ca2+](i), when observed, was only transient, while the stimulation of amylase release was sustained.