|
|
||||||||||||||||
| My research is centered primarily around the effects of dissolved gases on cardio-respiratory function in ectothermic vertebrates. My work has two broad objectives: (1) To characterize and try to understand how an anoxia-tolerant animal such as the freshwater turtle (Chrysemys picta) can function without oxygen. (2) To characterize and model some of the acid-base, cardiovascular, endocrine, and respiratory responses and limitations of white sturgeon (Acipenser transmontanus) and green sturgeon (A. medirostris) chronically exposed to environmental hypercapnia and hypoxia. The turtle project is comprehensive. It will require students to design and implement projects including, but not limited to; (1) Using static and flow-through respirometry to measure oxygen consumption rate, (2) Using surgically implanted ultrasonic flow probes for the direct measurement of cardiac output and regional blood flow distribution, (3) Using colored microspheres for indirect measurement of regional blood flow distribution. The sturgeon project includes both field-based and laboratory-based research. The field projects will involve telemetry so that students can remotely monitor movements and ecophysiological data (e.g. water temperature/depth, dissolved oxygen, heart rate) of white and green sturgeon in the San Francisco Bay and Sacramento-San Joaquin River Delta area. The laboratory studies will assess cardiorespiratory, endocrine, acid-base responses to environmental hypercapnia and hypoxia. The following is an example of a current project focus: Effects of changes in the ionic composition of the blood on myocardial activity in freshwater turtles. The orderly coordination of the electrical and mechanical events during the cardiac cycle allows a healthy heart to function effectively as a pump. In mammals, and other vertebrates, blood electrolyte concentration abnormalities, particularly potassium (K+) and calcium (Ca+2), can produce cardiac disability. Elevated plasma K+ levels cause changes ventricular repolarization and result in severe and often lethal cardiac abnormalities. Ventricular arrhythmias result when the plasma K+ level rises above normal (hyperkalemia), and at higher concentrations, results in paralysis of the atria and prolongation of the QRS. In short, as ECF [K+] rises, the pacemaker and myocardial resting membrane potentials decrease and the cells/fibers eventually become unexcitable, and the heart stops in diastole. Another potentially serious source of cardiac disability arises from elevated blood [Ca+2] (hypercalcemia). In short, increased ECF Ca+2 has a positive inotropic effect, shortens action potential duration, and accelerates depolarization. When ECF [Ca+2] is high, calcium rigor usually results. Painted turtles (Chrysemys picta) are semiaquatic freshwater turtles that are champion divers. They can survive submergence in normoxic water for at least 150 days while those in anoxic water can survive for a maximum of ca. 125 days. Below are data from a laboratory study (Ultsch et. al, 1999 P.B.Z. 72(4):493-501) showing predive blood plasma values for selected ions, compared with values obtained after the longest measured period of submergence survived by C. picta picta in normoxic and anoxic water.
Prolonged submergence in anoxic water renders the blood of a painted turtle hyperkalemic and hypercalcemic, yet the heart continues to beat and circulate the blood. The turtle?s adaptation to anoxia is extreme among the vertebrates and in my lab, we will investigate regulation of cardiac output and what influences the ability of the turtle heart to pump during these extreme conditions.
Last modified July 10, 2002 |
||||||||||||||||