title: Regulatory mechanisms and the role of calcium and potassium channels controlling supercontractile crop muscles in adult Phormia regina.
abstract: Bioassays and electrophysiological recordings were conducted in the adult blowfly Phormia regina to provide new insights into the regulatory mechanisms governing the crop filling and emptying processes of the supercontractile crop muscles. The cibarial pump drives ingestion. Simultaneous multisite extracellular recordings show that crop lobe (P5) distension during ingestion of a 4.7 μl sugar meal does not require muscle activity by any of the other pumps of the system. Conversely, pumping of fluids toward the anterior of the crop system during crop emptying is brought about by active muscle contraction, in the form of a highly coordinated peristaltic wave starting from P5 and progressively propagating to P6, P4 and P3 pumps, with P5 contracting with a frequency about 3.4 times higher than the other pumps. The crop contraction rate is also modulated by hemolymph-borne factors such as sugars, through ligand recognition at a presumptive receptor site rather than by an osmotic effect, as assessed by both behavioural and electrophysiological experiments. In this respect, sugars of equal osmolarity produce different effects, glucose being inhibitory and mannose ineffective for crop muscles, while trehalose enhances crop activity. Finally, voltage and current clamp experiments show that the muscle action potentials (mAPs) at the P4 pump are sustained by a serotonin-sensitive calcium conductance. Serotonin enhances calcium entry into the muscle cells and this could lead, as an indirect modulatory effect, to activation of a Ca(2+)-activated K(+) conductance (IK(Ca)), which sustains the following mAP repolarization phase in such a way that further mAPs can be generated early and the frequency consequently increased.
authors.affiliation: Department of Biomedical Sciences, University of Cagliari, University Campus, S.P. 8, I-09042 Monserrato (CA), Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Solari
authors.forename: John G
authors.initials: JG
authors.lastname: Stoffolano
authors.forename: Joanna
authors.initials: J
authors.lastname: Fitzpatrick
authors.forename: Alan
authors.initials: A
authors.lastname: Gelperin
authors.forename: Alan
authors.initials: A
authors.lastname: Thomson
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Talani
authors.forename: Enrico
authors.initials: E
authors.lastname: Sanna
authors.forename: Anna
authors.initials: A
authors.lastname: Liscia
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D004175:Diptera / Q000502:physiology*; D005260:Female; D041981:Gastrointestinal Tract / Q000502:physiology; D009132:Muscles / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D015221:Potassium Channels; D012701:Serotonin; D002118:Calcium
keywords: 5-HT; ACCR; AKH; Chemical vs. osmotic effect; DMS; Dipteran crop; Electrophysiology; Glucose/trehalose effect; Sodium/calcium inhibitors; Supercontractile muscles; adipokinetic hormone; average crop contraction rate; dromyosuppressin; mAP; muscle action potential; serotonin