Contractile activation in the retractor unguis muscle of the cockroach Periplaneta americana |
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| Institution: | 1. DMD Candidate, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA;2. Resident, Department of Oral and Maxillofacial Surgery, Louisiana State University Health Sciences Center, New Orleans, LA, USA;3. Resident, Division of Oral and Maxillofacial Surgery, UT Southwestern Medical Center, Dallas, TX, USA;4. Fellow, Department of Oral and Maxillofacial Surgery, Florida Craniofacial Institute, Tampa, FL, USA;5. Clinical Professor, Department of Oral and Maxillofacial Surgery and Pharmacology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA;6. Private Practice, Brockton Oral and Maxillofacial Surgery Inc., Brockton, MA, USA;7. Attending, Department of Oral and Maxillofacial Surgery, Good Samaritan Medical Center, Brockton, MA, USA;8. Visiting Professor, Department of Oral and Maxillofacial Surgery, Kaohsiung Medical University School of Dentistry, Kaohsiung City, Taiwan;9. Resident, Division of Oral and Maxillofacial Surgery, New York-Presbyterian/Columbia University Irving Medical Center, New York, NY, USA;10. Assistant Professor, Section Chief, Penn Presbyterian Hospital, Section Chief, Philadelphia Veterans Affairs Medical Center, Department of Oral and Maxillofacial Surgery and Pharmacology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA;11. Assistant Professor, Department of Oral and Maxillofacial Surgery and Pharmacology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA;1. Orofacial Development and Regeneration, Institute of Oral Biology, Centre of Dental Medicine, University of Zurich, Switzerland;2. Department of Clinical Sciences and Stomatology, Polytechnic University of Marche, Ancona, Italy |
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| Abstract: | 1. The K+-induced contracture consists of a phasic and a sustained component. Both were eliminated in Ca2+-free saline, but the sustained component recovered on the addition of Ca2+ to the muscle.2. Procaine mainly inhibited the phasic component. 3. Unlike the sustained component, the phasic component was inhibited by nifedipine in a concentration dependent manner.4. Divalent cations such as Mn2+, Co2+ and Ni2+ markedly increased the sustained component at low concentrations, but decreased it at high concentrations. The cations also modified the phasic component differentially, but to a lesser extent. High concentration abolished the phasic component.5. Ouabain markedly enhanced the sustained component.6. Caffeine contracture was a phasic type. Its duration and amplitude were augmented by pre-soaking the muscle in Na+-reduced salines. Immediate pre-treatment with caffeine eliminated the phasic component of the 160mM K+-induced contracture.7. These results suggest that a Na-Ca exchange mechanism may play a role in excitation-contraction coupling in insect muscle. Calcium ions flowing into the cell upon membrane depolarization may specifically activate the phasic component by way of a calcium-induced calcium releasing mechanism. |
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