RECORDING ION CHANNEL ACTIVITY IN SUPERIOR CERVICAL GANGLION NEURONS:POSSIBLE ROLE IN HYPERTENSION. 

Kiara Vann, Anne B. Jeffers and Jeffrey L. Overholt. Department of Life Sciences, WSSU.

Abstract Hypertension is high blood pressure, categorized as systolic pressure over 140 and

diastolic pressure over 90. Within the African-American community, there is a greater risk of developing hypertension and other cardiovascular diseases than any other ethnicity. The superior cervical ganglion (SCG) is part of the sympathetic nervous system that is responsible for preparing your body for “flight or fight” causing an increase in heart rate and blood pressure. A previous study suggested a link between hypertension and the SCG in a genetic model of hypertension, (mRen2)27 rats (Aileru, 2004). In this genetic model of hypertension, elevated Angiotensin II circulation in rats caused an increased activity in ganglionic transmission at the SCG, suggesting hypertension results from changes in sympathetic synaptic transmission at the SCG in (mRen2)27 rats. Therefore the purpose of our study is to understand the cellular mechanisms by which changes in the physiology of autonomic synaptic transmission contribute to this genetic form of hypertension. To this end we are using the whole-cell configuration of the patch clamp technique to record ionic current in SCG neurons from control and (mRen2)27 rats. Ionic currents through Na+, K+ and Ca2+ channels are responsible for electrical impulses in action potentials and therefore control the ganglionic transmission in the SCG. The overall aim of these studies is to identify possible therapeutic targets associated with genetic forms of hypertension.

Sympathetic Nervous System The sympathetic nervous system is part

of the autonomic nervous system. The sympathetic nervous system is responsible for preparing your body for “flight or fight. These include pupil dilation, increased sweating, increased heart rate, and increased blood pressure.

As noticed in the diagram, the sympathetic system is responsible for accelerating heartbeat ,releasing epinephrine and norepinephrine and constriction of blood vessels.

Superior Cervical Ganglion The superior cervical

ganglion is the largest of the cervical ganglia and is located on the posterior side of the internal carotid artery and internal jugular vein; both play key roles in supplying blood to the brain and heart.

Hypertension Hypertension is also known as high

blood pressure. Blood pressure is the force of your heart pumping blood against your arteries wall. Blood pressure is the highest during beating (systolic pressure). When the heart is at rest, blood pressure is falling (diastolic pressure). Hypertension is 140 over 90. Hypertension doesn’t have any symptoms but can lead to cardiovascular diseases such as stroke, heart failure, heart attack and aneurysm.

Hypertension Statistics

Age Men (%) Women (%)

20-34 9.2 2.235-44 21.1 12.645-54 36.2 36.255-64 50.2 54.465-74 64.1 70.875 and older 65.0 80.2

All 31.8 30.3

Race of Ethnic Group

Men (%) Women (%)

African American

s42.2 44.1

Mexican American

s24.8 28.6

Whites 31.2 28.3All 31.8 30.3

Women are about as likely as men to develop high blood pressure during their lifetimes. However, for people under 45 years old, the condition affects more men than women. For people 65 years and older, it affects more women than men.1

African Americans develop high blood pressure more often, and at an earlier age, than whites and Mexican Americans do. Among African Americans, more women than men have the condition.1

Scientific American, March 1992

1. Form an electrically tight seal (gigaseal) between glass electrode and cell membrane

Patch Clamp Technique:

Once seal is formed there are a number of possible recording configurations

250 pA20 ms

Patch Clamp Technique:

In addition to ionic current you can also measure:

Membrane Potential

10 sec

20 m

V

Neurotransmitter release

An action potential is an all or none. A stimulus causes sodium channel to open and sodium ions rushes inside. The neuron becomes more positive and depolarized. Once the potassium channel opens, the potassium rushes out the cell reversing the depolarization. The sodium channels start to close and the action potential returns to -70mv.

Channel types:

A. K+ channels:The most diverse group of channels1. Set the resting membrane potential close to EK2. Shape action potentials

B. Ca2+ Channels:Can be divided into 2 major groups, high and low

voltage activatedCa2+ acts as a second messenger in many diverse

processes including muscle contraction, neurotransmitter release and gene regulationNa+ and Cl- Channels

Questions