School of Pharmacy and Applied Science

Physiology and Pharmacology of Snail Heart

The common garden snail (Helix aspersa) has a 2 chambered heart with one auricle and one ventricle. This is a myogenic heart, not unlike that in the human. Yet the snail is a much more primitive animal that does not regulate its body temperature as well as estivating (hibernating) in harsh environmental conditions. Hence snail heart can adapt to periods of reduced oxygen uptake by the snail as well as very cold temperatures.

Initial studies have shown that snail heart has some areas that are more electrically excitable, while others require a chemical signal for activation of contraction. There are many chemicals that have been identified in snails that have neuroactive and cardioactive properties. My work is involved in further characterising the properties of some of these cardioactive compounds (ie. FMRFamide, Small CardioActive Peptide B) in the auricle and ventricle.

Several project students have investigated the effects of temperature on cardiac activation in snail heart; how temperature alters the calcium requirements for initiation of contraction and subsequent strength of the heart beat (and heart rate)and basic pharmacology (dose dependence curves) for cardioactive agents such as adrenaline, noradrenaline, acetylcholine, atropine, dopamine, FMRFamide and Small Cardioactive Peptide B.

This year we will be investigating the distribution of receptors for these cardioactive agents in the auricle and ventricle of snail heart. This will involve some histochemistry, electron microscopy and antibody binding techniques to map the different receptor types.

Recently this work has developed into a collaboration with David Morton and Michael Nott to investigate the effects of iron molluscicides (such as FeEDTA) on cardiac muscle in the snail.

Calcium Loading and Release Properties of Cardiac Sarcoplasmic Reticulum.
Sarcoplasmic Reticulum (SR) in muscle tissue is modified endoplasmic reticulum (ER) that stores and releases calcium during muscle contraction. In skeletal muscle the SR is much more highly developed than in cardiac muscle, but in both muscle types SR is absolutely essential for regulating calcium movements in the myoplasm and reaching the contractile proteins during the contraction~relaxation cycle.

Using funtionally skinned (sarcolemma rendered leaky), the properties of calcium loading and release by cardiac SR can be studied in very small multicellular preparations from the right ventricle of rat heart.

While many of the properties of SR calcium loading and release in cardiac muscle are now well understood, we are still learning more. Recently we showed in this laboratory that the calcium capacity of cardiac SR in functionally skinned ventricular prepartions is very different when the muscle is skinned in the presence of different concentrations of calcium buffering solutions (based on the calcium chelating compound EGTA).

These studies confirmed the contention that the amoung of calcium that can be loaded and subsequently released by cardiac SR depends on whether the calcium loading occurs under "quiescent" or resting conditions, compared with "working" or active conditions. In essence this means that the amount of calcium stored and released by the SR varies in part depending on whether the heart is at rest (diastolic) or working (systolic).

Many laboratories use different calcium buffering conditions during the preration of their muscle for study, so this information is very important to help us understand why we may see very different results for what may be apparently the same set of conditions.

This work has been done in collaboration with the Muscle Research Group, La Trobe University.