Effects of secretagogues on cytosolic Ca super(2+) levels in rat submandibular granular ducts and acini

In the present study, microfluorometric methods were employed to examine the responses of intracellular Ca super(2+) concentration ((Ca super(2+)) sub(i)) in individual male rat submandibular acini and intralobular (granular) ducts to various fluid secretory stimuli. We show that granular ducts respond to muscarinic (carbachol) and alpha -adrenergic (epinephrine) stimulation by increasing (Ca super(2+)) sub(i) in a manner that is qualitatively similar to acini, but that in contrast to acini, these ducts do not respond to substance P. Because the transduction of a substance P peptidergic signal typically occurs via increased (Ca super(2+)) sub(i), this observation suggests that there are no substance P receptors on granular ducts. Ducts were also found to be somewhat more responsive to both carbachol and epinephrine than acini. Although muscarinic, alpha -adrenergic, and vasoactive intestinal peptide (VIP) stimulation are known to induce the secretion of epidermal growth factor from granular ducts, no significant increase in ductal (Ca super(2+)) sub(i) in response to VIP was observed.