HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 102/2/901    most recent 91209.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Klose, M. K. Articles by Atwood, H. L. PubMed PubMed Citation Articles by Klose, M. K. Articles by Atwood, H. L.

Role of ATP-Dependent Calcium Regulation in Modulation of Drosophila Synaptic Thermotolerance

¹Department of Physiology, University of Toronto, Toronto; ²Department of Biology, Queen's University, Biosciences Complex, Kingston; and ³Program in Developmental and Stem Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada

Submitted 12 November 2008; accepted in final form 8 May 2009

Maintenance of synaptic transmission requires regulation of intracellular Ca²⁺ in presynaptic nerve terminals; loss of this regulation at elevated temperatures may cause synaptic failure. Accordingly, we examined the thermosensitivity of presynaptic calcium regulation in Drosophila larval neuromuscular junctions, testing for effects of disrupting calcium clearance. Motor neurons were loaded with the ratiometric Ca²⁺ indicator Fura-dextran to monitor calcium regulation as temperature increased. Block of the Na⁺/Ca²⁺ exchanger or removal of extracellular Ca²⁺ prevented the normal temperature-induced increase in resting calcium. Conversely, two treatments that interfered with Ca²⁺ clearance—inactivation of the endoplasmic reticulum Ca²⁺-ATPase with thapsigargin and inhibition of the plasma membrane Ca²⁺-ATPase with high pH—significantly accelerated the temperature-induced rise in resting Ca²⁺ concentration and reduced the thermotolerance of synaptic transmission. Disrupting Ca²⁺-ATPase function by interfering with energy production also facilitated the temperature-induced rise in resting [Ca²⁺] and reduced thermotolerance of synaptic transmission. Conversely, fortifying energy levels with extra intracellular ATP extended the operating temperature range of both synaptic transmission and Ca²⁺ regulation. In each of these cases, Ca²⁺ elevations evoked by an electrical stimulation of the nerve (evoked Ca²⁺ responses) failed when resting Ca²⁺ remained >e 200 nM for several minutes. Failure of synaptic function was correlated with the release of intracellular calcium stores, and we provide evidence suggesting that release from the mitochondria disrupts evoked calcium responses and synaptic transmission. Thus the thermal limit of synaptic transmission may be directly linked to the stability of ATP-dependent mechanisms that regulate intracellular ion concentrations in the nerve terminal.