Mechanical stimulation increases intracellular calcium concentration in nodose sensory neurons

The cellular mechanisms involved in activation of mechanosensitive visceral sensory nerves are poorly understood. The major goal of this study was to determine the effect of mechanical stimulation on intracellular calcium concentration ([Ca2+]i) using nodose sensory neurons grown in culture. Primary cultures of nodose sensory neurons were prepared by enzymatic dispersion from nodose ganglia of 4-8 week old Sprague-Dawley rats. Whole cell [Ca2+]i was measured by a microscopic digital image analysis system in fura-2 loaded single neurons. Brief mechanical stimulation of individual nodose sensory neurons was achieved by deformation of the cell surface with a glass micropipette. In 31 of 50 neurons (62%), mechanical stimulation increased [Ca2+]i from 125 +/- 8 to 763 +/- 89 nM measured approximately 10 s after stimulation. [Ca2+]i then declined gradually, returning to near basal levels over a period of minutes. [Ca2+]i failed to increase after mechanical stimulation in the remaining 19 neurons. The mechanically-induced rise in [Ca2+]i was essentially abolished after the neurons were incubated for 5-10 min in zero Ca2+ buffer (n = 7) or after addition of gadolinium (10 microM), a blocker of stretch-activated ion channels (n = 5). The effect of gadolinium was reversed after removal of gadolinium. The results indicate that: (1) mechanical stretch increases [Ca2+]i in a subpopulation of nodose sensory neurons in culture, and (2) the stretch-induced increase in [Ca2+]i is dependent on influx of Ca2+ from extracellular fluid and is reversibly blocked by gadolinium. The findings suggest that opening of stretch-activated ion channels in response to mechanical deformation leads to an increase in Ca2+ concentration in visceral sensory neurons.(ABSTRACT TRUNCATED AT 250 WORDS)