Oscillations of cytosolic Ca2+ in pituitary cells due to action potentials

Abstract

Electrical activity in non-neuronal cells can be induced by altering the membrane potential and eliciting action potentials. For example, hormones, nutrients and neurotransmitters act on excitable endocrine cells. In an attempt to correlate such electrical activity with regulation of cell activation, we report here direct measurements of cytosolic free Ca2+ changes coincident with action potentials. This was achieved by the powerful and novel combination of two complex techniques, the patch clamp and microfluorimetry using fura 2 methodology. Changes in intracellular calcium concentration were monitored in single cells of the pituitary line GH3B6. We show that a single action potential leads to a marked transient increase in cytosolic free calcium. The size of these short-lived maxima is sufficient to evoke secretory activity. The striking kinetic features of these transients enabled us to identify oscillations in intracellular calcium concentration in unperturbed cells resulting from spontaneous action potentials, and hence provide an explanation for basal secretory activity. Somatostatin, an inhibitor of pituitary function, abolishes the spontaneous spiking of free cytosolic Ca2+ which may explain its inhibitory effect on basal prolactin secretion. Our data therefore demonstrate that electrical activity can stimulate Ca2+-dependent functions in excitable non-neuronal cells.

The Relationship between Spontaneous Calcium Oscillations and Cell Proliferation in Cultured Smooth Muscle Cells.

“…Ca 21 os cillations are induced by hormonal stimulations and mito genic stimulations in many cell types, and spontaneous Ca 21 oscillations have been observed in several kinds of cells (5,6), including cardiac myocytes. Previously we also found spontaneous Ca 21 oscillations in 25% to 80% of cultured smooth muscle cells obtained from guinea pig ileum (7).…”

Measurement of cytosolic free Ca2+ in individual pancreatic acini

“…It has been documented that some cell types are characterized by the presence of spontaneous [Ca2+]i oscillations [19,[24][25][26]. Under basal conditions, i.e.…”

“…A typical fluorescence recording from an individual acinus stimulated with caerulein 100 pM is shown in fig. 1 [6,16,19,23]. A slight decrease in the fluorescence intensity was observed at the two excitation wavelengths, a phenomenon probably due to photobleaching of fura-2, since basal fluorescence of acini did not decrease markedly with increasing the time elapsed from loading.…”

“…The equipment available in our laboratory has been described in greater detail in previous publications [19,20]. The microscope, connected to a photometre and a photomultiplier tube, is contained in a thermostatted box at 37°C.…”

“…Fura-2 signals were calibrated by determining the ratio between the fluorescence emission intensities (at 505 nm) of the probe excited at two different wavelengths: 340 nm (F340) and 380 nm (F3so) [6,17,23]. From the ratio R = F34o/F38o, values of [Ca2+]i were calculated according to the equation used in [19]:…”