Calcium feedback mechanisms regulate oscillatory activity of a TRP-like Ca2+ conductance in C. elegans intestinal cells.
Inositol-1,4,5-trisphosphate (IP3)-dependent Ca2+ oscillations in Caenorhabditis elegans intestinal epithelial cells regulate the nematode defecation cycle. The role of plasma membrane ion channels in intestinal cell oscillatory Ca2+ signalling is unknown. We have shown previously that cultured intestinal cells express a Ca2+-selective conductance, I(ORCa), that is biophysically similar to TRPM7 currents. I(ORCa) activates slowly and stabilizes when cells are patch clamped with pipette solutions containing 10 mm BAPTA and free Ca2+ concentrations of approximately 17 nm. However, when BAPTA concentration is lowered to 1 mm, I(ORCa) oscillates. Oscillations in channel activity induced simultaneous oscillations in cytoplasmic Ca2+ levels. Removal of extracellular Ca2+ inhibited I(ORCa) oscillations, whereas readdition of Ca2+ to the bath caused a rapid and transient reactivation of the current. Experimental manoeuvres that elevated intracellular Ca2+ blocked current oscillations. Elevation of intracellular Ca2+ in the presence of 10 mm BAPTA to block I(ORCa) oscillations led to a dose-dependent increase in the rate of current activation. At intracellular Ca2+ concentrations of 250 nm, current activation was transient. Patch pipette solutions buffered with 1-4 mm of either BAPTA or EGTA gave rise to similar patterns of I(ORCa) oscillations. We conclude that changes in Ca2+ concentration close to the intracellular opening of the channel pore regulate channel activity. Low concentrations of Ca2+ activate the channel. As Ca2+ enters and accumulates near the pore mouth, channel activity is inhibited. Oscillating plasma membrane Ca2+ entry may play a role in generating intracellular Ca2+ oscillations that regulate the C. elegans defecation rhythm.
Estevez
Ana Y
AY
Vanderbilt University Medical Center, T-4202 Medical Center North, Nashville, TN 37232-2520, USA.
Strange
Kevin
K
D000818:Animals; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D025461:Feedback, Physiological / Q000502:physiology; D007413:Intestinal Mucosa / Q000166:cytology* / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D050052:TRPC Cation Channels
D029742:Caenorhabditis elegans Proteins; D015220:Calcium Channels; D050052:TRPC Cation Channels