|Nachman, Ronald - Ron|
Submitted to: American Journal of Physiology - Regulatory Integrative & Comparative Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/8/2010
Publication Date: 8/11/2010
Citation: Schepel, S.A., Fox, A.J., Miyauchi, J.T., Sou, T., Yang, J.D., Lau, K., Blum, A.W., Nicholson, L.K., Tiburcy, F., Nachman, R.J., Piermarini, P.M., Beyenbach, K.W. 2010. The single kinin receptor signals to separate and independent physiological pathways in Malpighian tubules of the yellow fever mosquito. American Journal of Physiology - Regulatory Integrative & Comparative Physiology. 299:R612-R622. Interpretive Summary: Because of problems with the development of resistance to conventional pesticides, there is a critical need for new concepts and alternative approaches in controlling insect pests. The basic premise of this research is that neuropeptides (short chains of amino acids) serve as potent messengers in insects to regulate vital functions. Nevertheless, neuropeptides in and of themselves hold little promise as pest control agents because of susceptibility to being degraded in the target pest. New, selective control measures may be developed by designing metabolically stable mimics of these neuropeptides that interact with the active site within the agricultural or medical pest in such a way as to either inhibit or over-stimulate critical neuropeptide-regulated life functions. We report on the development of biostable versions of neuropeptides of the insect kinin class that have been shown to potently interact in a selective fashion with the active site in the yellow fever mosquito that regulates water balance. The experiments demonstrate for the first time that two separate and independent pathways are activated when the natural kinin hormones bind to the active site: one pathway triggers water secretion itself and the other triggers electrical activity of the organ involved in water balance. One synthetic version of the kinin hormone selectively triggers one of these pathways and another selectively triggers the other pathway. The work increases our understanding of the mechanisms of water balance regulation in mosquitoes; information that can be used to design methods to selectively disrupt this critical regulatory activity in these disease vectors. The work brings us one step closer to the development of practical neuropeptide-like substances that will be effective in controlling pest mosquitoes in an environmentally friendly fashion.
Technical Abstract: In the past we have used the leucokinins, the kinins of the cockroach Leucophaea, to evaluate the mechanism of diuretic action of kinin peptides in Malpighian tubules of the yellow fever mosquito Aedes aegypti. Now using aedeskinins, the kinins of Aedes, are available, we find that in isolated Aedes Malpighian tubules all three aedeskinins (1µM) significantly 1) increase the rate of fluid secretion 2) hyperpolarize the basolateral membrane voltage (V), and 3) decrease the input resistance (R) of principal cells, consistent with the known increase in the Cl- conductance of the paracellular pathway. Aedeskinin-III, which we studied in further detail, significantly increases fluid secretion with an EC50 of 3.4 x 10-8 M. In parallel, the Na+ concentration in secreted fluid significantly decreases, the K+ concentration significantly increases, while the concentration of Cl- remains unchanged. Whereas the three aedeskinins triggered effects on both electrophysiology (V, R) and fluid secretion, most synthetic kinins (which contain modifications of the C-terminal amide pentapeptide core sequence critical for biological activity) displayed independent effects on either electrophysiology or fluid secretion. Taken together, the data suggest that two separate signaling pathways are activated when kinins bind to their receptor: one triggers electrophysiological events and the other triggers fluid secretion. It remains to be determined whether both of these signaling pathways emanate from a single kinin receptor via a conformational phenomenon, such as agonist-directed signaling, or from two distinct functional forms of the kinin receptor that may arise via differential glycosylation.