title: Calcium store depletion activates two distinct calcium entry pathways in secretory cells of the blowfly salivary gland.
abstract: Ca2+ influx into secretory cells of the intact salivary gland of the blowfly Calliphora erythrocephala elicited by the agonist 5-hydroxytryptamine (5-HT) or the Ca2+ uptake inhibitor thapsigargin was studied by using Fura-2 and digital fluorescence imaging and by recordings of the transepithelial potential. Application of saturating [5-HT] in the absence of Ca2+ (Ca2+o) from the bathing saline did not affect the initial Ca2+ transient but greatly attenuated the subsequent sustained Ca2+ elevation observed in the presence of Ca2+o demonstrating that the latter component of the [Ca2+]i response is largely dependent on Ca2+ entry across the baso-lateral plasma membrane. La3+ or Gd3+ (10 microM) mimicked the effects of the withdrawal of Ca2+o. Experimental attempts temporally to uncouple 5-HT stimulation and Ca2+ influx by withdrawal of Ca2+o during agonist application revealed a second Ca2+ entry pathway. This pathway was insensitive to 10 microM La3+ and produced transient [Ca2+]i increases whose amplitudes were a function of the [5-HT] during the preceding stimulation and that were selectively suppressed by 50 microM SK&F 96365. Both (10 microM) La(3+)-insensitive [Ca2+]i transients and (10 microM) La3+ inhabitable tonic [Ca2+]i increases could be sequentially activated in the presence of 5-HT or thapsigargin (1 microM). These results indicate that Ca2+ store depletion by 5-HT or thapsigargin activates two distinct store-operated Ca2+ entry pathways, one of which supports tonic [Ca2+]i increases. The other is transiently activated, even under conditions that prohibit store refilling and does not significantly contribute to the [Ca2+]i responses evoked by saturating 5-HT concentrations.
authors.affiliation: Institut für Zoophysiologie und Zellbiologie, Universität Potsdam, Germany. zimmerm@rz.uni-potsdam.de
authors.forename: B
authors.initials: B
authors.lastname: Zimmermann
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004175:Diptera / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005682:Gadolinium / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007811:Lanthanum / Q000494:pharmacology; D008861:Microsomes / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D012469:Salivary Glands / Q000737:chemistry / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D007093:Imidazoles; D012701:Serotonin; D004533:Egtazic Acid; D019284:Thapsigargin; D007811:Lanthanum; D005682:Gadolinium; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium