Patch-clamp-induced perturbations of [Ca2+](i) activity in somatotropes

Somatotropes and GC cells, a GH-producing cell line, exhibit [Ca2+](i) osci llations that result from rhythmic Ca2+ action potentials. Determination of this operating mode required simultaneous recording of both parameters by fura-2 imaging and patch-clamp techniques. In order to test whether patch r ecording induces artificial alteration of the [Ca2+](i) oscillatory pattern , we recorded separately or simultaneously [Ca2+](i) and membrane potential . In the absence of any other stimulation, seal formation in patch-clamp re cording evoked by itself a 2.5- to 4-fold persistent increase in basal [Ca2 +](i), speeded up their frequency (from 0.03-0.17 to 0.4 Hz) and changed th eir pattern to a tonic mode. Patch-induced [Ca2+](i) increase was reproduce d by mechanical contact between the pipette and the membrane. It was reduce d by nifedipine, a blocker of L-type Ca2+ channels, as well as by removal o f external Na+, It was fully blocked by external Ca2+ removal or gadolinium . All patch-clamp-induced perturbations were reversed by membrane hyperpola rization. We propose that patch-clamp recording evokes Ca2+ entry through L -type Ca2+ channels either directly, or indirectly via membrane depolarizat ion. This shows that patch recordings in endocrine cells showing mechanosen sitivity have to be interpreted with caution, and explains why long-lasting patch recordings are so difficult to obtain. Copyright (C) 1999 S. Karger AG, Basel.