Loren Haarsma -- Research Interests

Electrophysiology

Three co-PIs and I have recently received a grant from the National Science Foundation to set up an electrophysiology lab at Calvin College and work on the following projects.

Neuronal development and the Rho family of small GTPases

Stem cells have the ability to become other types of cells, including nerve cells. PC12 cells can be used to study this transition because, when cultured with Nerve Growth Factor (NGF), they become more nerve-like in at least three ways. (1) They stop dividing. (2) They grow long processes similar to axons and dendrites. (3) They become more electrically excitable. Previous research showed that if, prior to addition of NGF, PC12 cells are transfected with DNA which up-regulates the protein RhoA, the up-regulated RhoA prevents NGF from causing the first two changes. We are using patch clamp techniques to study the third change. Preliminary results show that, perhaps surprisingly, up-regulating RhoA does not appear to prevent the increase in electrical excitability associated with neuronal development. We will use transfection techniques to up- and down-regulate other members of the Rho family of small GTPases to study what effect (if any) they have on the development of electrical excitability. (This work is being done in collaboration with Prof. Stephen Matheson of Calvin College's Biology Department.)
Poster on RhoA results.
Poster on Y-compound results.
Caveat: Results on these posters have been presented to colleagues and at conferences, but have not yet been published in a peer-reviewed journal.

Lacrimal gland duct cells and the potassium content of tears

Tear fluid is much more than just water. Tears provide an appropriate combination of ions, growth factors, signaling molecules, and other biological molecules which continually bathe the surface of the eye. This fluid is essential for the health and proper functioning of the eye. Lacrimal glands produce the aqueous component of the tears. The lacrimal gland is primarily composed of acinar secretory cells which secrete a protein-rich fluid with an electrolyte composition similar to normal extracellular fluid. Acinar secretory cells empty into ducts that are composed of a single layer of epithelial cells. These ducts do not merely conduct the lacrimal gland fluid, but they appear to modify it – especially its ion content. This is apparent from the fact the tears have a potassium ion concentration more than four times higher than in the fluid produced by the acinar cells. If these duct cells are actively involved in the secretion and modification of the lacrimal fluid, it is expected that they will express ion transporters and ion channels that are uniquely involved in this process. It is also expected that this process is regulated by the nervous system, and therefore certain types of neurotransmitter receptors should be expressed on the duct cells. We are using electrophysiology techniques to investigate ion channels and neurotransmitter receptors in these duct cells. (This work is being done in collaboration with Prof. John Ubels of Calvin College's Biology Department.)
Poster on UV-activated K+ currents in corneal epithelial cells.
Caveat: Results on this poster have been presented to colleagues and at the ARVO 2008 conference, but have not yet been published in a peer-reviewed journal.

Amacrine cells of the retina

My postdoctoral research at the Retinal Microcircuitry Lab of the University of Pennsylvania studied the functions of a certain class of retinal nerve cells -- the "spiking" amacrine cells. I plan to continue studying the functional circuitry of spiking amacrine cells -- how they receive inputs, how they transmit information to ganglion cells, and what types of information they encode. Details: Most retinal amacrine cells do not appear to "spike." (That is, they do not appear to fire the traveling "action potentials" typical of most nerve cells). However, certain types of amacrine cells have long axon-like processes which spread laterally over long distances (several millimeters) in the inner plexiform layer of the retina. These "wide-field" amacrine cells (and perhaps a few other types of amacrine cells) do appear to fire action potentials. It has long been known that retinal ganglion cells receive information about visual stimulation over these distances, and we wondered whether wide-field amacrines were responsible. We used tetrodotoxin to block action potentials in an intact in vitro retina, and intracellularly recorded the activity of ganglion cells which receive inputs from these spiking amacrine cells. Two important results are (1) Action potentials are necessary to transmit visual information to ganglion cells over long distances (more than a millimeter), implicating the spiking wide-field amacrine cells. (2) A few minutes after all action potentials in the retina were blocked, ganglion cell responses to visual stimulation increased. Thus, the over-all sensitivity of the retina to visual stimulation is controlled, to some extent, by the continual activity of spontaneously spiking cells. I plan to continue these studies into the functional circuitry of amacrine cells and the role they play in encoding visual information.

Investigation of possible neuronal function for Probst’s bundles

Agenesis of the corpus callosum (ACC) is a congenital defect. In some human and animal types, neuronal fibers which ordinarily would cross the midline during fetal development instead run in a rostral-to-caudal direction and terminate in the ipsilateral cortex, forming Probst’s bundles (PB). Despite its potential clinical importance, no study to date has established the physiological or behavioral significance of these fibers. We will use the electrophysiology rig to study tissue slices from PBs from a mouse strain which consistently exhibits ACC. We will investigate if the PB axons conduct action potentials, if the fibers become functional GABAergic neurons, and if they result in inhibitory or excitatory post-synaptic potentials on their targets. (This work will be done in collaboration with Prof. Paul Moes of Calvin College's Psychology Department.)

My curriculum vitae.

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(Last updated 2008 April 25)