Somatotropes and GC cells, a GH-producing cell line, exhibit [Ca<sup>2+</sup>]<sub>i</sub> oscillations that result from rhythmic Ca<sup>2+</sup> 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 recording induces artificial alteration of the [Ca<sup>2+</sup>]<sub>i</sub> oscillatory pattern, we recorded separately or simultaneously [Ca<sup>2+</sup>]<sub>i</sub> and membrane potential. In the absence of any other stimulation, seal formation in patch-clamp recording evoked by itself a 2.5- to 4-fold persistent increase in basal [Ca<sup>2+</sup>]<sub>i</sub>, speeded up their frequency (from 0.03–0.17 to 0.4 Hz) and changed their pattern to a tonic mode. Patch-induced [Ca<sup>2+</sup>]<sub>i</sub> increase was reproduced by mechanical contact between the pipette and the membrane. It was reduced by nifedipine, a blocker of L-type Ca<sup>2+</sup> channels, as well as by removal of external Na<sup>+</sup>. It was fully blocked by external Ca<sup>2+</sup> removal or gadolinium. All patch-clamp-induced perturbations were reversed by membrane hyperpolarization. We propose that patch-clamp recording evokes Ca<sup>2+</sup> entry through L-type Ca<sup>2+</sup> channels either directly, or indirectly via membrane depolarization. This shows that patch recordings in endocrine cells showing mechanosensitivity have to be interpreted with caution, and explains why long-lasting patch recordings are so difficult to obtain.