Slow motility in hair cells of the frog amphibian papilla: myosin light chain-mediated shape change.
Using video, fluorescence and confocal microscopy, quantitative analysis and modeling, we investigated intracellular processes mediating the calcium/calmodulin (Ca(2+)/CaM)-dependent slow motility in hair cells dissociated from the rostral region of amphibian papilla, one of the two auditory organs in frogs. The time course of shape changes in these hair cells during the period of pretreatment with several specific inhibitors, as well as their response to the calcium ionophore, ionomycin, were recorded and compared. These cells respond to ionomycin with a tri-phasic shape change: an initial phase of iso-volumetric length decrease; a period of concurrent shortening and swelling; and the final phase of increase in both length and volume. We found that both the myosin light chain kinase inhibitor, ML-7, and antagonists of the multifunctional Ca(2+)/CaM-dependent kinases, KN-62 and KN-93, inhibit the iso-volumetric shortening phase of the response to ionomycin. The type 1 protein phosphatase inhibitors, calyculin A and okadaic acid induce minor shortening on their own, but do not significantly alter phase 1 response. However, they appear to counter effects of the inhibitors of Ca(2+)/CaM-dependent kinases. We hypothesize that an active actomyosin-based process mediates the iso-volumetric shortening in the frog rostral amphibian papillar hair cells.
Department of Physiological Science, 621 Charles E. Young Drive S., University of California, Los Angeles, CA 90095-1606, USA. farahbak@ucla.edu
Nasser A
NA
Farahbakhsh
Peter M
PM
Narins
D000205:Actomyosin / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002465:Cell Movement / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D048429:Cell Size; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D007476:Ionophores / Q000737:chemistry; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D008954:Models, Biological; D018994:Myosin Light Chains / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism; D009925:Organ of Corti / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D054645:Protein Phosphatase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D011894:Rana pipiens; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors
D004791:Enzyme Inhibitors; D007476:Ionophores; D018994:Myosin Light Chains; D000205:Actomyosin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D009219:Myosin-Light-Chain Kinase; D054645:Protein Phosphatase 1; D043263:Myosin-Light-Chain Phosphatase; D002118:Calcium