Spontaneous Ca2+ Signaling of Interstitial Cells in the Guinea Pig Prostate

Purpose: We investigated whether prostate interstitial cells generate spontaneous Ca2+ oscillation, a proposed mechanism underlying pacemaker potentials to drive spontaneous activity in stromal smooth muscle cells. Materials and Methods: Intracellular free Ca2+ in portions of guinea pig prostate and freshly isolated, single prostate interstitial cells were visualized using fluo-4 Ca2+ fluorescence. Spontaneous electrical activity was recorded in situ with intracellular microelectrodes. Results: In whole tissue preparations spontaneous Ca2+ flashes firing synchronously across all smooth muscle cells within the field of view resulted in muscle wall contractions. Nonpropagating Ca2+ waves were also recorded in individual smooth muscle cells. Nifedipine (Sigma (R)) (1 mu M) largely decreased or abolished these Ca2+ flashes and suppressed slow wave discharge upon blockade of their superimposed action potentials. Isolated prostate interstitial cells were readily distinguished from smooth muscle cells by their spiky processes and lack of contraction during intracellular Ca2+ increases. Prostate interstitial cells generated spontaneous Ca2+ transients in the form of whole cell flashes, intracellular Ca2+ waves or localized Ca2+ sparks. All 3 Ca2+ signals were abolished by nicardipine (1 mu M), cyclopiazonic acid (10 mu M), caffeine (Sigma) (10 mM) or extracellular Ca2+ removal. Conclusions: Prostate interstitial cells generate spontaneous Ca2+ transients that occur at a frequency comparable to Ca2+ flashes in situ or slow waves relying on functional internal Ca2+ stores. However, unlike other interstitial cells in the urinary tract, Ca2+ influx through L-type Ca2+ channels is fundamental to Ca2+ transient firings in prostate interstitial cells. Thus, it is not possible to conclude that prostate interstitial cells are responsible for pacemaker potential generation.